t/t7NNN: 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>

t/t7421-submodule-summary-add.sh

@@ -12,6 +12,10 @@ while making sure to add submodules using `git submodule add` instead of
 
 . ./test-lib.sh
 
+test_expect_success 'setup' '
+	git config --global protocol.file.allow always
+'
+
 test_expect_success 'summary test environment setup' '
 	git init sm &&
 	test_commit -C sm "add file" file file-content file-tag &&