Fix jgit not closed during clone

[jonesbusy]

Should fix #103

Ensuring jgit is closed after clone

I'm not sure if there is other places

Testing done

Got CredentialsProvider when cloning many plugin.

Was not able to reproduce after this fix

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• Ensure that the pull request title represents the desired changelog entry
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[gounthar]

Very interesting, I will check this on Gitpod.
Thanks,!

[gounthar]

So far so good for me, thanks a bunch! 🤗

[gounthar]

For the time being, I only had one error:

Forking and cloning plugin commons-text-api locally from repo commons-text-api-plugin 
Forking the repository to personal account... 
Repository forked to personal account successfully. 
Failed to process plugin: commons-text-api 
org.eclipse.jgit.api.errors.TransportException: https://github.com/gounthar/commons-text-api-plugin.git: Authentication is required but no CredentialsProvider has been registered
        at org.eclipse.jgit.api.FetchCommand.call(FetchCommand.java:249)
        at org.eclipse.jgit.api.CloneCommand.fetch(CloneCommand.java:319)
        at org.eclipse.jgit.api.CloneCommand.call(CloneCommand.java:189)
        at io.jenkins.tools.pluginmodernizer.core.github.GHService.fetchRepository(GHService.java:141)
        at io.jenkins.tools.pluginmodernizer.core.github.GHService.forkCloneAndCreateBranch(GHService.java:74)
        at io.jenkins.tools.pluginmodernizer.core.impl.PluginModernizer.start(PluginModernizer.java:54)
        at io.jenkins.tools.pluginmodernizer.cli.Main.run(Main.java:181)
        at picocli.CommandLine.executeUserObject(CommandLine.java:2030)
        at picocli.CommandLine.executeHelpRequest(CommandLine.java:2016)
        at picocli.CommandLine.executeHelpRequest(CommandLine.java:1987)
        at picocli.CommandLine$AbstractParseResultHandler.execute(CommandLine.java:2272)
        at picocli.CommandLine$RunLast.execute(CommandLine.java:2421)
        at picocli.CommandLine.execute(CommandLine.java:2174)
        at io.jenkins.tools.pluginmodernizer.cli.Main.main(Main.java:42)
Caused by: org.eclipse.jgit.errors.TransportException: https://github.com/gounthar/commons-text-api-plugin.git: Authentication is required but no CredentialsProvider has been registered
        at org.eclipse.jgit.transport.TransportHttp.connect(TransportHttp.java:687)
        at org.eclipse.jgit.transport.TransportHttp.openFetch(TransportHttp.java:465)
        at org.eclipse.jgit.transport.FetchProcess.executeImp(FetchProcess.java:153)
        at org.eclipse.jgit.transport.FetchProcess.execute(FetchProcess.java:105)
        at org.eclipse.jgit.transport.Transport.fetch(Transport.java:1480)
        at org.eclipse.jgit.api.FetchCommand.call(FetchCommand.java:238)
        ... 13 common frames omitted
Forking and cloning plugin configuration-as-code locally from repo configuration-as-code-plugin 

[gounthar]

And another...

Forking and cloning plugin pipeline-graph-analysis locally from repo pipeline-graph-analysis-plugin 
Forking the repository to personal account... 
Repository forked to personal account successfully. 
Failed to process plugin: pipeline-graph-analysis 
org.eclipse.jgit.api.errors.TransportException: https://github.com/gounthar/pipeline-graph-analysis-plugin.git: Authentication is required but no CredentialsProvider has been registered
        at org.eclipse.jgit.api.FetchCommand.call(FetchCommand.java:249)
        at org.eclipse.jgit.api.CloneCommand.fetch(CloneCommand.java:319)
        at org.eclipse.jgit.api.CloneCommand.call(CloneCommand.java:189)
        at io.jenkins.tools.pluginmodernizer.core.github.GHService.fetchRepository(GHService.java:141)
        at io.jenkins.tools.pluginmodernizer.core.github.GHService.forkCloneAndCreateBranch(GHService.java:74)
        at io.jenkins.tools.pluginmodernizer.core.impl.PluginModernizer.start(PluginModernizer.java:54)
        at io.jenkins.tools.pluginmodernizer.cli.Main.run(Main.java:181)
        at picocli.CommandLine.executeUserObject(CommandLine.java:2030)
        at picocli.CommandLine.executeHelpRequest(CommandLine.java:2016)
        at picocli.CommandLine.executeHelpRequest(CommandLine.java:1987)
        at picocli.CommandLine$AbstractParseResultHandler.execute(CommandLine.java:2272)
        at picocli.CommandLine$RunLast.execute(CommandLine.java:2421)
        at picocli.CommandLine.execute(CommandLine.java:2174)
        at io.jenkins.tools.pluginmodernizer.cli.Main.main(Main.java:42)
Caused by: org.eclipse.jgit.errors.TransportException: https://github.com/gounthar/pipeline-graph-analysis-plugin.git: Authentication is required but no CredentialsProvider has been registered
        at org.eclipse.jgit.transport.TransportHttp.connect(TransportHttp.java:687)
        at org.eclipse.jgit.transport.TransportHttp.openFetch(TransportHttp.java:465)
        at org.eclipse.jgit.transport.FetchProcess.executeImp(FetchProcess.java:153)
        at org.eclipse.jgit.transport.FetchProcess.execute(FetchProcess.java:105)
        at org.eclipse.jgit.transport.Transport.fetch(Transport.java:1480)
        at org.eclipse.jgit.api.FetchCommand.call(FetchCommand.java:238)
        ... 13 common frames omitted
Forking and cloning plugin pipeline-graph-view locally from repo pipeline-graph-view-plugin