Make sure TestSitePath exist before creating .htkey

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MR should be updated for 10.1

Also IS should be updated as it references acquia dev desktop which support stopped in June 2021.

I've actually recently run into this issue, and I have some more details that affected me here I wanted to share...

The fix here still solves my problem, and I can explain why as well.

So I ran into this issue with the following scenario...
* I am installing a site that uses a custom cron job to make a call out to an RSS feed, download the file, and store it locally for processing by the feeds module.
* Drupal core runs through the INSTALL steps... but the install_configure_form step actually hardens the simpletest site directory, and sets the folder to 555 (not writeable).
* Drupal core at the end of the installation then triggers a cron. My job calls out to the internet. Drupal core has a custom testing middleware that intercepts that calls, and tries to add testing headers to the call, and ultimately calls drupal_generate_test_ua(), which tries to write the .htkey file to a hardened sites directory, and that fails... so my first cron run fails silently.

I actually came across this b/c by enabling the "locale" module, the call to drupal_generate_test_ua() was made earlier in the stack, before the hardening, and the .htkey file gets placed successfully, and there is no more failure.