Add access rules for build tests

Automatic updates module uses a version strings (with periods in them) for its testing. Here's the diff of what I do over top of BTB to get those tests to pass.

diff --git a/core/tests/Drupal/BuildTests/Framework/BuildTestBase.php b/core/tests/Drupal/BuildTests/Framework/BuildTestBase.php
index f698998f87..3b95aa78cd 100644
--- a/core/tests/Drupal/BuildTests/Framework/BuildTestBase.php
+++ b/core/tests/Drupal/BuildTests/Framework/BuildTestBase.php
@@ -411,6 +411,9 @@ protected function instantiateServer($port, $working_dir = NULL) {
       '-t',
       $working_path,
     ];
+    if (file_exists($working_path . DIRECTORY_SEPARATOR . '.ht.router.php')) {
+      $server[] = $working_path . DIRECTORY_SEPARATOR . '.ht.router.php';
+    }
     $ps = new Process($server, $working_path);
     $ps->setIdleTimeout(30)
       ->setTimeout(30)

Let's start the discussion.

Given 8.5.x is already not supported, and definitely not by the time 8.8.x ships, do we need the conditional?

Also, this may be a silly question, but is there anyway to test this? That's a pretty glaring bug to not use a file we're depending on, no?

We can't always be sure how folks will use build tests. They might want to use it with 1) non-drupal install 2) very old drupal install 3) something else I can't think of where the router doesn't exist.

There is a way to test it and I can add a test.

Interdiff is the tests only patch. Note, this pulls in quickstart base from #3082230: [meta] Convert some tests to Build tests. Which just means that meta will need a re-roll if it lands here first.

I really muffed up that test only patch. Here are updated patches.

Yeah, tests passed.

Committed and pushed f6b2481aee to 9.0.x and 2a58c7ef79 to 8.9.x. Thanks!

Will backport this to 8.8.x once the code freeze is over.

Discussed with @catch we agreed this was good to backport to 8.8.x