t/lib-submodule-update.sh: allow local submodules

To prepare for changing the default value of `protocol.file.allow` to
"user", update the `prolog()` function in lib-submodule-update to allow
submodules to be cloned over the file protocol.

This is used by a handful of submodule-related test scripts, which
themselves will have to tweak the value of `protocol.file.allow` in
certain locations. Those will be done in subsequent commits.

Signed-off-by: Taylor Blau <me@ttaylorr.com>

t/lib-submodule-update.sh

@@ -196,6 +196,7 @@ test_git_directory_exists () {
 # the submodule repo if it doesn't exist and configures the most problematic
 # settings for diff.ignoreSubmodules.
 prolog () {
+	test_config_global protocol.file.allow always &&
 	(test -d submodule_update_repo || create_lib_submodule_repo) &&
 	test_config_global diff.ignoreSubmodules all &&
 	test_config diff.ignoreSubmodules all