fetch: add a test for --force flag

There are two ways to force-fetch tags that have changed: either by
specifying an explicit forced ref (+refs/tags/*:refs/tags/*), or by
using --force.

The first approach was already tested, but the second was not. This
has now been addressed.

Author: orgads

t/t5516-fetch-push.sh

@@ -1105,7 +1105,10 @@ test_force_fetch_tag () {
 			git commit -m 'file1' &&
 			git tag $tag_args testTag &&
 			test_must_fail git -C ../child1 fetch origin tag testTag &&
-			git -C ../child1 fetch origin '+refs/tags/*:refs/tags/*'
+			git -C ../child1 fetch origin '+refs/tags/*:refs/tags/*' &&
+			git tag $tag_args testTag HEAD^ &&
+			test_must_fail git -C ../child1 fetch origin tag testTag &&
+			git -C ../child1 fetch --force origin tag testTag
 		)
 	"
 }