chore(wpmc S2): pin patchwork cache + tighten noop test guard

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitignore

@@ -1,4 +1,5 @@
 /vendor/
+/vendor/.patchwork-cache/
 /composer.lock
 /dist/
 /.phpunit.result.cache

patchwork.json

@@ -1,3 +1,4 @@
 {
-  "redefinable-internals": ["function_exists"]
+  "redefinable-internals": ["function_exists"],
+  "cache-path": "vendor/.patchwork-cache"
 }

tests/FieldGroupTest.php

@@ -19,12 +19,18 @@ final class FieldGroupTest extends TestCase
 
     public function test_do_register_is_noop_when_acf_missing(): void
     {
-        \Brain\Monkey\Functions\when('function_exists')->justReturn(false);
+        \Brain\Monkey\Functions\when('function_exists')->alias(function ($name) {
+            return $name !== 'acf_add_local_field_group';
+        });
         \Brain\Monkey\Functions\expect('acf_add_local_field_group')->never();
 
         FieldGroup::do_register();
 
-        self::assertTrue(true, 'do_register must not call acf_add_local_field_group when ACF is missing');
+        // The real check is the ->never() Mockery expectation above (verified at
+        // teardown). assertTrue is here only to keep PHPUnit from flagging the
+        // test as risky under failOnRisky="true" — Mockery assertions don't
+        // count toward PHPUnit's assertion tally.
+        self::assertTrue(true);
     }
 
     public function test_do_register_calls_acf_add_local_field_group_with_expected_structure(): void