Bump tested up to and automate future bumps

[pwtyler]

• Bumps "Tested up to"
• Automates future "Tested up to" bumps

As this project uses the asset-only action, this works with PRs to release instead of our normal develop workflow.

A few notes

• This project does not use the prepare-dev action, so "Tested up to" changes still need to be merged to develop (that action probably needs to be updated to handle this correctly anyway)
• I think the branch config is redundant, as release is the default branch on this project, but seeking clarification Docs clarification— if branch not yet, does it use main, or default/current branch (if default is something else) jazzsequence/action-validate-plugin-version#13

https://getpantheon.atlassian.net/browse/SITE-2845

[jazzsequence]

defining release if it's already the repository default should be redundant but it doesn't hurt.