Ops: GitHub release page fix [skip ci]

Each release was showing something odd for commits, for example:
 released this 9 days ago · 0 commits to
 7cfce4bfc7eaafce8c79749633a38df6c6479529 since this release

The GitHub docs say I shouldn't need to specify commitish for a release,
but it seems I do, at least for the way I am releasing.

Verified on test-doc-blocks and carried over here.

Commits oddity should no longer appear for next releases.

Author: lread

.github/workflows/release.yml

@@ -75,3 +75,4 @@ jobs:
       with:
         tag_name: ${{ steps.target-version.outputs.tag}}
         release_name: ${{ steps.target-version.outputs.tag}}
+        commitish: main