Fix missing non-zero exit code for failure cases in test.mjs

The two affected code paths caught and logged errors, but that wasn't
reflected in the exit code of the process, and that is what GitHub
Actions (and other tools) to determine if process execution was
successful or not. This commit fixes the issue by making sure we
consistently exit with code 1 in case of errors so that GitHub Actions
pipelines correctly reflect the outcome of the test run.

Author: timvandermeij

test/test.mjs

@@ -1148,6 +1148,7 @@ async function startBrowsers({ baseUrl, initializeSession, numSessions = 1 }) {
         })
         .catch(function (ex) {
           console.log(`Error while starting ${browserName}: ${ex.message}`);
+          session.numErrors = 1;
           closeSession(sessionName);
         });
     }
@@ -1395,6 +1396,7 @@ async function main() {
     // because the teardown logic of the tests did not get a chance to run.
     console.error(e);
     await Promise.all(sessions.map(session => closeSession(session.name)));
+    process.exit(1);
   }
 }