t5551: stop writing packed-refs directly

We have multiple tests in t5551 that write thousands of tags. To do so
efficiently we generate the tags by writing the `packed-refs` file
directly, which of course assumes that the reference database is backed
by the files backend.

Refactor the code to instead use a single `git update-ref --stdin`
command to write the tags. While the on-disk end result is not the same
as we now have a bunch of loose refs instead of a single packed-refs
file, the distinction shouldn't really matter for any of the tests that
use this helper.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

t/t5551-http-fetch-smart.sh

@@ -359,7 +359,9 @@ create_tags () {
 
 	# now assign tags to all the dangling commits we created above
 	tag=$(perl -e "print \"bla\" x 30") &&
-	sed -e "s|^:\([^ ]*\) \(.*\)$|\2 refs/tags/$tag-\1|" <marks >>packed-refs
+	sed -e "s|^:\([^ ]*\) \(.*\)$|create refs/tags/$tag-\1 \2|" <marks >input &&
+	git update-ref --stdin <input &&
+	rm input
 }
 
 test_expect_success 'create 2,000 tags in the repo' '