Don't try to sign git commits when running tests

I have git set up to always sign with a key that requires a password, this would
require me to enter that password when running tests.
Git allows overwriting config for a single invocation, lets just do that

test/rbs/collection/sources/git_test.rb

@@ -56,6 +56,8 @@ def test_resolved_revision_updated_after_fetch
       git "init", chdir: origin_repo
       git "config", "user.email", "[email protected]", chdir: origin_repo
       git "config", "user.name", "Your Name", chdir: origin_repo
+      # Ignore potential signing key protected by passphrase
+      git "config", "commit.gpgsign", "false", chdir: origin_repo
       git "checkout", "-b", "main", chdir: origin_repo
 
       git "commit", "--allow-empty", "-m", "Initial commit", chdir: origin_repo