Index: docker-compose.yml
===================================================================
--- docker-compose.yml	(revision 53345)
+++ docker-compose.yml	(working copy)
@@ -41,6 +41,8 @@
       - LOCAL_PHP_MEMCACHED=${LOCAL_PHP_MEMCACHED-false}
       - PHP_FPM_UID=${PHP_FPM_UID-1000}
       - PHP_FPM_GID=${PHP_FPM_GID-1000}
+      - GITHUB_REF=${GITHUB_REF-false}
+      - GITHUB_EVENT_NAME=${GITHUB_EVENT_NAME-false}
 
     volumes:
       - ./tools/local-env/php-config.ini:/usr/local/etc/php/conf.d/php-config.ini
Index: tests/phpunit/includes/abstract-testcase.php
===================================================================
--- tests/phpunit/includes/abstract-testcase.php	(revision 53345)
+++ tests/phpunit/includes/abstract-testcase.php	(working copy)
@@ -202,8 +202,8 @@
 	/**
 	 * Allows tests to be skipped on some automated runs.
 	 *
-	 * For test runs on GitHub Actions for something other than trunk/master,
-	 * we want to skip tests that only need to run for master.
+	 * For test runs on GitHub Actions for something other than trunk,
+	 * we want to skip tests that only need to run for trunk.
 	 */
 	public function skipOnAutomatedBranches() {
 		// https://docs.github.com/en/free-pro-team@latest/actions/reference/environment-variables#default-environment-variables
@@ -210,12 +210,12 @@
 		$github_event_name = getenv( 'GITHUB_EVENT_NAME' );
 		$github_ref        = getenv( 'GITHUB_REF' );
 
-		if ( $github_event_name && 'false' !== $github_event_name ) {
+		if ( $github_event_name ) {
 			// We're on GitHub Actions.
 			$skipped = array( 'pull_request', 'pull_request_target' );
 
-			if ( in_array( $github_event_name, $skipped, true ) || 'refs/heads/master' !== $github_ref ) {
-				$this->markTestSkipped( 'For automated test runs, this test is only run on trunk/master' );
+			if ( in_array( $github_event_name, $skipped, true ) || 'refs/heads/trunk' !== $github_ref ) {
+				$this->markTestSkipped( 'For automated test runs, this test is only run on trunk' );
 			}
 		}
 	}
Index: tests/phpunit/tests/basic.php
===================================================================
--- tests/phpunit/tests/basic.php	(revision 53345)
+++ tests/phpunit/tests/basic.php	(working copy)
@@ -8,7 +8,7 @@
 class Tests_Basic extends WP_UnitTestCase {
 
 	public function test_license() {
-		// This test is designed to only run on trunk/master.
+		// This test is designed to only run on trunk.
 		$this->skipOnAutomatedBranches();
 
 		$license = file_get_contents( ABSPATH . 'license.txt' );
@@ -18,7 +18,7 @@
 	}
 
 	public function test_security_md() {
-		// This test is designed to only run on trunk/master.
+		// This test is designed to only run on trunk.
 		$this->skipOnAutomatedBranches();
 
 		$security = file_get_contents( dirname( ABSPATH ) . '/SECURITY.md' );
Index: tests/phpunit/tests/external-http/basic.php
===================================================================
--- tests/phpunit/tests/external-http/basic.php	(revision 53345)
+++ tests/phpunit/tests/external-http/basic.php	(working copy)
@@ -10,7 +10,7 @@
 	 * @covers ::wp_remote_retrieve_body
 	 */
 	public function test_readme_php_version() {
-		// This test is designed to only run on trunk/master.
+		// This test is designed to only run on trunk.
 		$this->skipOnAutomatedBranches();
 
 		$readme = file_get_contents( ABSPATH . 'readme.html' );
@@ -31,7 +31,7 @@
 	 * @covers ::wp_remote_retrieve_body
 	 */
 	public function test_readme_mysql_version() {
-		// This test is designed to only run on trunk/master.
+		// This test is designed to only run on trunk.
 		$this->skipOnAutomatedBranches();
 
 		$readme = file_get_contents( ABSPATH . 'readme.html' );
@@ -63,7 +63,7 @@
 	 * @covers ::wp_remote_retrieve_body
 	 */
 	public function test_readme_mariadb_version() {
-		// This test is designed to only run on trunk/master.
+		// This test is designed to only run on trunk.
 		$this->skipOnAutomatedBranches();
 
 		$readme = file_get_contents( ABSPATH . 'readme.html' );
Index: tests/phpunit/tests/theme.php
===================================================================
--- tests/phpunit/tests/theme.php	(revision 53345)
+++ tests/phpunit/tests/theme.php	(working copy)
@@ -213,7 +213,7 @@
 	 * @ticket 48566
 	 */
 	public function test_year_in_readme() {
-		// This test is designed to only run on trunk/master.
+		// This test is designed to only run on trunk.
 		$this->skipOnAutomatedBranches();
 
 		foreach ( $this->default_themes as $theme ) {