RATIS-2570. Minor improvements in make_rc.sh

[adoroszlai]

What changes were proposed in this pull request?

Make some minor improvements in make_rc.sh:

• print actual release version, not snapshot one
• check GPG key sooner
• merge 3 loops over *.tar.gz
• skip empty commit
• fix typos

https://issues.apache.org/jira/browse/RATIS-2570

How was this patch tested?

Before:

Prepare release artifacts for Apache Ratis 3.3.0-SNAPSHOT

After:

Prepare release artifacts for Apache Ratis 0.0.1-ci-test

Tested that creating two subsequent RCs does not add empty versioning commits:

Prepare release artifacts for Apache Ratis 0.0.1-rc2
...
++ git commit -a -m '[RELEASE] Update version to 0.0.1'
On branch release-0.0.1
nothing to commit, working tree clean
++ echo '<version> up to date, nothing to commit'
<version> up to date, nothing to commit
...
HEAD is now at a8758c5f [RELEASE] Update version to 0.0.1
...

release check in CI:
https://github.com/adoroszlai/ratis/actions/runs/28117851656/job/83261844311

[szetszwo]

+1 the change looks good.

[adoroszlai]

Thanks @szetszwo for the review.