t0610: pass fully qualified branch name to update-ref

We create several sample branches by doing "git update-ref branch-$i".
But update-ref requires a fully qualified name, so this is creating
"branch-$i" at the root of the ref namespace, not actual branches in
"refs/heads/".

The test doesn't care either way. It is about reftable compaction, and
the ref creation is just to trigger the creation of new reftables.
But to future-proof it against update-ref getting more picky about
creating top-level refs, let's do the more normal thing and create
actual branches.

Author: peff

t/t0610-reftable-basics.sh

@@ -347,11 +347,11 @@ test_expect_success 'ref transaction: env var disables compaction' '
 	for i in $(test_seq $iterations)
 	do
 		GIT_TEST_REFTABLE_AUTOCOMPACTION=false \
-		git -C repo update-ref branch-$i HEAD || return 1
+		git -C repo update-ref refs/heads/branch-$i HEAD || return 1
 	done &&
 	test_line_count = $expected repo/.git/reftable/tables.list &&
 
-	git -C repo update-ref foo HEAD &&
+	git -C repo update-ref refs/heads/foo HEAD &&
 	test_line_count -lt $expected repo/.git/reftable/tables.list
 '