fix: Correct quoting in GitUsernamePasswordBinding

[gabyx]

JENKINS-27082 - Quote the username and password in credentials binding

Followup an better solution to: #1310

Fix wrong quoting in askpass.

Won't solve all cases of quoting but will avoid some common problems related to quoting. For example, if the username or password includes a single quote, then the added quoting will fail. For the more common cases where the username or password contains a special special character that is not a single quote, this pull request will be an improvement.

Checklist

• I have read the CONTRIBUTING doc
• I have referenced the Jira issue related to my changes in one or more commit messages
• I have added tests that verify my changes
• Unit tests pass locally with my changes
• I have added documentation as necessary
• No Javadoc warnings were introduced with my changes
• No spotbugs warnings were introduced with my changes
• Documentation in README has been updated as necessary
• Online help has been added and reviewed for any new or modified fields
• I have interactively tested my changes
• Any dependent changes have been merged and published in upstream modules (like git-client-plugin)

Types of changes

Correct quoting in bash script.

• Dependency or infrastructure update
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

[MarkEWaite]

Fixed in #1443 . Thanks for reporting the issue!