t/t4NNN: 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/t4059-diff-submodule-not-initialized.sh

@@ -49,7 +49,7 @@ test_expect_success 'setup - submodules' '
 '
 
 test_expect_success 'setup - git submodule add' '
-	git submodule add ./sm2 sm1 &&
+	git -c protocol.file.allow=always submodule add ./sm2 sm1 &&
 	commit_file sm1 .gitmodules &&
 	git diff-tree -p --no-commit-id --submodule=log HEAD -- sm1 >actual &&
 	cat >expected <<-EOF &&