t/2NNNN: allow local submodules

To prepare for the default value of `protocol.file.allow` to change to
"user", ensure tests that rely on local submodules can initialize them
over the file protocol.

Tests that only need to interact with submodules in a limited capacity
have individual Git commands annotated with the appropriate
configuration via `-c`. Tests that interact with submodules a handful of
times use `test_config_global` instead. Test scripts that rely on
submodules throughout use a `git config --global` during a setup test
towards the beginning of the script.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
diff --git a/t/t2400-worktree-add.sh b/t/t2400-worktree-add.sh
index 5a74954..cd02f78 100755
--- a/t/t2400-worktree-add.sh
+++ b/t/t2400-worktree-add.sh
@@ -597,6 +597,7 @@
 '
 
 test_expect_success '"add" with uninitialized submodule, with submodule.recurse unset' '
+	test_config_global protocol.file.allow always &&
 	test_create_repo submodule &&
 	test_commit -C submodule first &&
 	test_create_repo project &&
@@ -612,6 +613,7 @@
 '
 
 test_expect_success '"add" with initialized submodule, with submodule.recurse unset' '
+	test_config_global protocol.file.allow always &&
 	git -C project-clone submodule update --init &&
 	git -C project-clone worktree add ../project-4
 '