message: [tests] Allow for multiple probes
  The `probes` in the vercel.json files in tests fixtures weren't allowing both `mustContain` _and_ `responseHeaders` probes due to an `else` block. This PR allows to combine those checks into the same probe test.
diff: @@ -177,12 +177,15 @@ async function runProbe(probe, deploymentId, deploymentUrl, ctx) {
  const { text, resp } = await fetchDeploymentUrl(probeUrl, fetchOpts);
  logWithinTest('finished testing', JSON.stringify(probe));
  + let hadTest = false;
  +
  if (probe.status) {
  if (probe.status !== resp.status) {
  throw new Error(
  `Fetched page ${probeUrl} does not return the status ${probe.status} Instead it has ${resp.status}`
  );
  }
  + hadTest = true;
  }
  if (probe.mustContain || probe.mustNotContain) {
  @@ -204,7 +207,10 @@ async function runProbe(probe, deploymentId, deploymentUrl, ctx) {
  ` Response headers:\n ${headers}`
  );
  }
  - } else if (probe.responseHeaders) {
  + hadTest = true;
  + }
  +
  + if (probe.responseHeaders) {
  // eslint-disable-next-line no-loop-func
  Object.keys(probe.responseHeaders).forEach(header => {
  const actual = resp.headers.get(header);
  @@ -226,6 +232,7 @@ async function runProbe(probe, deploymentId, deploymentUrl, ctx) {
  );
  }
  });
  + hadTest = true;
  } else if (probe.notResponseHeaders) {
  Object.keys(probe.notResponseHeaders).forEach(header => {
  const headerValue = resp.headers.get(header);
  @@ -241,9 +248,10 @@ async function runProbe(probe, deploymentId, deploymentUrl, ctx) {
  );
  }
  });
  - } else if (!probe.status) {
  - assert(false, 'probe must have a test condition');
  + hadTest = true;
  }
  +
  + assert(hadTest, 'probe must have a test condition');
  }
  async function testDeployment(
  