fix: [gapic-generator-java] update year to 2023 in generated license headers

[emmileaf]

Similar to #951: updates copyright year in generated license headers to 2023 (for new files):

• Template string change in CommentComposer.java
• Golden file updates in unit/integration/showcase tests

[sonarqubecloud]

[gapic-generator-java-root] Kudos, SonarCloud Quality Gate passed!   

0 Bugs
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No Coverage information
0.0% Duplication

[sonarqubecloud]

[java_showcase_integration_tests] Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[sonarqubecloud]

[java_showcase_unit_tests] Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[blakeli0]

CC: @suztomo This is what I meant that the generator generates license headers, but not to the protoc generated files. I guess we need to update owlbot to 2023 somewhere? Because I see that the newly generated client still have 2022, like this.

[suztomo]

These are the implementation of the post processor. https://github.com/googleapis/synthtool/blob/master/docker/owlbot/java/src/fix-license-headers.py https://github.com/googleapis/synthtool/blob/master/synthtool/languages/java.py#L117 It has "2020" (https://github.com/googleapis/synthtool/blob/70ec2609beefb006579939d8231acdfb6c32fe5a/synthtool/languages/java.py#L32).

[emmileaf]

Oh, I see the corresponding 2020 year in generated proto- and grpc- classes: e.g. RapidMigrationAssessmentGrpc.java; Annotation.java.

Will merge this PR and follow-up separately with the fix in synthtool repo. Thanks @blakeli0 and @suztomo!