Show a warning annotation when "master" branch usage is detected

That way, both the web UI and the email from GitHub will show
the recommendation about to move to the new "main" branch.

Also, unrelated, exclude some unreachable code from code coverage
analysis.

src/Command/CopyPasteDetectorCommand.php

@@ -38,6 +38,7 @@ protected function configure(): void
 
     protected function execute(InputInterface $input, OutputInterface $output): int
     {
+        // @codeCoverageIgnoreStart
         if (!defined('PHPUNIT_TEST')) { // Only show deprecation warnings in non-test environments.
             trigger_deprecation(
                 'moodle-plugin-ci',
@@ -51,6 +52,7 @@ protected function execute(InputInterface $input, OutputInterface $output): int
                     'is deprecated and will be removed in 5.0.0. No replacement is planned.' . PHP_EOL;
             }
         }
+        // @codeCoverageIgnoreEnd
 
         $timer = new Timer();
         $timer->start();

src/Command/InstallCommand.php

@@ -62,6 +62,13 @@ protected function configure(): void
         $extra  = getenv('EXTRA_PLUGINS_DIR') !== false ? getenv('EXTRA_PLUGINS_DIR') : null;
         $node   = getenv('NODE_VERSION') !== false ? getenv('NODE_VERSION') : null;
 
+        // Emit a warning/annotation under GHA if the branch is master (recommending to move to main).
+        if (getenv('GITHUB_ACTIONS') && $branch === 'master') {
+            echo '::warning title=`master` branch use detected::The `master` branch of Moodle has been ' .
+                'moved to `main` and will stop working soon. Please consider moving to `main` in your ' .
+                'workflows. Ref.: MDLSITE-7418' . PHP_EOL;
+        }
+
         // As there is not only Travis CI, it can also be passed a generic environment variable.
         if (null === $plugin) {
             $plugin = getenv('CI_BUILD_DIR') !== false ? getenv('CI_BUILD_DIR') : null;