RATIS-2248. Rename CI workflows to .yaml

[adoroszlai]

What changes were proposed in this pull request?

Rename CI workflows to .yaml as suggested in #1219 (review)

https://issues.apache.org/jira/browse/RATIS-2248

How was this patch tested?

https://github.com/adoroszlai/ratis/actions/runs/13257613914

[szetszwo]

@adoroszlai , thanks a lot for working on this!

There are two more cases:

-- ./.github/workflows/post-commit.yml ----------------------------------------
 32:     uses: ./.github/workflows/ci.yml
   1 occurrence(s)
-- ./dev-support/checks/shellcheck.sh -----------------------------------------
 29:   | grep -v -e target/ -e node_modules/ -e '\.\(ico\|py\|yml\)$' \
   1 occurrence(s)

[adoroszlai]

Thanks @szetszwo for the review.

-- ./.github/workflows/post-commit.yml ----------------------------------------
 32:     uses: ./.github/workflows/ci.yml
   1 occurrence(s)

post-commit.yml no longer exists (was renamed), so this must be some leftover from master. The PR also changes the reference to ci.yml.

-- ./dev-support/checks/shellcheck.sh -----------------------------------------
 29:   | grep -v -e target/ -e node_modules/ -e '\.\(ico\|py\|yml\)$' \
   1 occurrence(s)

shellcheck.sh is unused, I'll file a task to remove it.

[szetszwo]

+1 the change looks good.