Add automated tests for CSS syntax checking #5586
Description
Is your feature request related to a problem? Please describe.
As evident by #5585, we do not have sufficient protections in place to detect/prevent change that
We currently have very little precautions in place
Describe the solution you'd like
An automated test added that checks that the css syntax of the css injected into blockly-common-style is valid (checking the css in the style tags after Blockly.inject call).
Describe alternatives you've considered
Adding checks to Blockly.Css.inject as an additional precaution. This would add addition protection, but it would not address the issue of detecting problems in tests.
Additional context