Update integration test constraint checking

Author: Anna Gringauze

webdev/test/integration_test.dart

@@ -162,7 +162,7 @@ name: sample
                   break;
                 case 'build_web_compilers':
                   webCompilersVersion = version;
-                  supportedRange = '^4.0.0';
+                  supportedRange = '^$_supportedWebCompilersVersion';
                   break;
                 case 'build_daemon':
                   buildDaemonVersion = version;