fix ListGroupsCommand and more phpt fies

Author: mondrake

src/TextUI/Command/Commands/ListGroupsCommand.php

@@ -70,13 +70,13 @@ public function execute(): Result
         );
 
         foreach ($groups as $group => $numberOfTests) {
-            if (str_starts_with($group, '__phpunit_')) {
+            if (str_starts_with((string) $group, '__phpunit_')) {
                 continue;
             }
 
             $buffer .= sprintf(
                 ' - %s (%d test%s)' . PHP_EOL,
-                $group,
+                (string) $group,
                 $numberOfTests,
                 $numberOfTests > 1 ? 's' : '',
             );

tests/end-to-end/cli/listing-tests-and-groups/list-groups-exclude-filter.phpt

@@ -15,5 +15,6 @@ require_once __DIR__ . '/../../../bootstrap.php';
 --EXPECTF--
 PHPUnit %s by Sebastian Bergmann and contributors.
 
-Available test group:
+Available test groups:
+ - 3 (1 test)
  - two (1 test)

tests/end-to-end/cli/listing-tests-and-groups/list-groups-exclude-group.phpt

@@ -16,5 +16,6 @@ require_once __DIR__ . '/../../../bootstrap.php';
 PHPUnit %s by Sebastian Bergmann and contributors.
 
 Available test groups:
+ - 3 (1 test)
  - default (1 test)
  - two (1 test)

tests/end-to-end/cli/listing-tests-and-groups/list-groups-include-filter.phpt

@@ -15,5 +15,6 @@ require_once __DIR__ . '/../../../bootstrap.php';
 --EXPECTF--
 PHPUnit %s by Sebastian Bergmann and contributors.
 
-Available test group:
+Available test groups:
+ - 3 (1 test)
  - two (1 test)

tests/end-to-end/cli/listing-tests-and-groups/list-groups.phpt

@@ -14,6 +14,7 @@ require_once __DIR__ . '/../../../bootstrap.php';
 PHPUnit %s by Sebastian Bergmann and contributors.
 
 Available test groups:
+ - 3 (1 test)
  - default (1 test)
  - one (1 test)
  - two (1 test)

tests/end-to-end/cli/listing-tests-and-groups/list-tests-exclude-filter.phpt

@@ -15,6 +15,6 @@ require_once __DIR__ . '/../../../bootstrap.php';
 --EXPECTF--
 PHPUnit %s by Sebastian Bergmann and contributors.
 
-Available test:
+Available tests:
  - PHPUnit\TestFixture\ListingTestsAndGroups\ExampleTest::testTwo
  - PHPUnit\TestFixture\ListingTestsAndGroups\ExampleTest::testThree