Use -diff built-in command for checking go mod tidy

[syjn99]

What type of PR is this?

Other

What does this PR do? Why is it needed?

https://go.dev/doc/go1.23

We can use -diff flag that was added in 1.23 to check go mod tidy. Deleting obsolete gomodtidy custom action and inlined the checker in go.yml.

Which issues(s) does this PR fix?

N/A

Other notes for review

Tested locally with messing up go.mod like:

echo 'require golang.org/x/fake v0.0.0' >> go.mod
go mod tidy -diff
echo $?

Acknowledgements

• I have read CONTRIBUTING.md.
• I have included a uniquely named changelog fragment file.
• I have added a description with sufficient context for reviewers to understand this PR.
• I have tested that my changes work as expected and I added a testing plan to the PR description (if applicable).