tag-git: accommodate for upstream's .txt -> .adoc rename

This is the gazillionth follow-up to that rename; It was noticed in
git-for-windows/build-extra#607 that this needed
yet another adjustement, this time in Git for Windows' release notes. In
that PR, the `please.sh` script was adjusted, which indeed used to be
how the release notes generation was automated.

In the meantime, we have moved from an Azure Pipelines-based
automation to a GitHub Actions-based automation, and the `please.sh`
script is no longer used to generate those; Instead the
`update-scripts/tag-git.sh` script in this here repository is used for
that purpose.

Therefore, the latter script needs to be adjusted, too.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

update-scripts/tag-git.sh

@@ -55,8 +55,8 @@ else
 		if ! grep -q "^\\* Comes with \\[Git $base_tag\\]" "$build_extra_dir"/ReleaseNotes.md
 		then
 			url=https://github.com/git/git/blob/$base_tag &&
-			txt="$(echo "${base_tag#v}" | sed 's/-rc[0-9]*$//').txt" &&
-			url=$url/Documentation/RelNotes/$txt &&
+			adoc="$(echo "${base_tag#v}" | sed 's/-rc[0-9]*$//').adoc" &&
+			url=$url/Documentation/RelNotes/$adoc &&
 			release_note="Comes with [Git $base_tag]($url)." &&
 			(cd "$build_extra_dir" && node ./add-release-note.js --commit feature "$release_note")
 		fi