Index: tests/phpunit/tests/rest-api/rest-plugins-controller.php
===================================================================
--- tests/phpunit/tests/rest-api/rest-plugins-controller.php	(revision 49907)
+++ tests/phpunit/tests/rest-api/rest-plugins-controller.php	(working copy)
@@ -1023,6 +1023,13 @@
 			10,
 			3
 		);
+
+		// Remove upgrade hooks which are not required for plugin installation tests
+		// and may interfere with the results due to unnecessary external HTTP requests.
+		remove_action( 'upgrader_process_complete', array( 'Language_Pack_Upgrader', 'async_upgrade' ), 20 );
+		remove_action( 'upgrader_process_complete', 'wp_version_check' );
+		remove_action( 'upgrader_process_complete', 'wp_update_plugins' );
+		remove_action( 'upgrader_process_complete', 'wp_update_themes' );
 	}
 
 	/**