t: mark tests regarding git-pack-refs(1) to be backend specific

Both t1409 and t3210 exercise parts of git-pack-refs(1). Given that we
must check the on-disk files to verify whether the backend has indeed
packed refs as expected those test suites are deeply tied to the actual
backend that is in use.

Mark the test suites to depend on the REFFILES backend.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Reviewed-by: Christian Couder <christian.couder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t1409-avoid-packing-refs.sh

@@ -5,6 +5,12 @@ test_description='avoid rewriting packed-refs unnecessarily'
 TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
+if test_have_prereq !REFFILES
+then
+  skip_all='skipping files-backend specific pack-refs tests'
+  test_done
+fi
+
 # Add an identifying mark to the packed-refs file header line. This
 # shouldn't upset readers, and it should be omitted if the file is
 # ever rewritten.

t/t3210-pack-refs.sh

@@ -15,6 +15,12 @@ export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
+if test_have_prereq !REFFILES
+then
+  skip_all='skipping files-backend specific pack-refs tests'
+  test_done
+fi
+
 test_expect_success 'enable reflogs' '
 	git config core.logallrefupdates true
 '