chore: script/most-recent-nightly-tag uses https rather than ssh repo URL (#2951)

The https URL suffices, and does not require that the caller has an
appropriate ssh key.

script/most-recent-nightly-tag.sh

@@ -4,7 +4,7 @@
 tag_prefix="nightly-"
 
 # Fetch all tags from the remote repository
-git fetch git@github.com:leanprover/lean4-nightly.git --tags > /dev/null
+git fetch https://github.com/leanprover/lean4-nightly.git --tags > /dev/null
 
 # Get the most recent commit that has a matching tag
 tag_name=$(git tag --merged HEAD --list "${tag_prefix}*" | sort -rV | head -n 1 | sed "s/^$tag_prefix//")