Switch to my own images, with dependencies satisfied

Necessary PHP modules, as well as Composer, are provided in the new images: https://git.ethitter.com/docker/images/container_registry.

tests/bootstrap.php

@@ -12,7 +12,9 @@ if ( ! $camo_tests_dir ) {
 }
 
 if ( ! file_exists( $camo_tests_dir . '/includes/functions.php' ) ) {
+	// @codingStandardsIgnoreStart
 	echo "Could not find $camo_tests_dir/includes/functions.php, have you run bin/install-wp-tests.sh ?" . PHP_EOL; // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped
+	// @codingStandardsIgnoreEnd
 	exit( 1 );
 }