Use ubuntu 20 for workflows

[tomjn]

Ubuntu 18 is deprecated and gives warnings, also cache vagrant boxes

Checks

• I've updated the changelog.
• I've tested this PR
• This PR is for the develop branch not the stable branch.
• This PR is complete and ready for review.

[update-docs]

Thanks for opening this pull request! Make sure CHANGELOG.md gets updated with this change, additionally any docs that need updated can be found at https://github.com/Varying-Vagrant-Vagrants/varyingvagrantvagrants.org

GitHub

GitHub - Varying-Vagrant-Vagrants/varyingvagrantvagrants.org: The VVV docs and website

The VVV docs and website. Contribute to Varying-Vagrant-Vagrants/varyingvagrantvagrants.org development by creating an account on GitHub.

[tomjn]

Looks like the MacOS 11 image doesn't have vagrant built in, do we need to use MacOS for all of them? Ubuntu might result in easier/quicker workflows with more availability

[tomjn]

 ▷ Running after_composer hook
 * [PHPCS]: Provisioning PHP_CodeSniffer (phpcs), see https://github.com/squizlabs/PHP_CodeSniffer

In JsonFile.php line 198:
                                                                         
  The file "/home/runner/.config/composer/config.json" is not readable. 

[tomjn]

I'm leaving the MacOS issue for another time as this change lets us do basic tests with Ubuntu 20