Missing embedded syntax definitions should not fail CI run

[deathaxe]

In case a syntax embeds 3rd-party syntaxes, which are not available while running syntax tests, following error messages are printed to console.

Error loading embed in syntax file "HTML (Astro).sublime-syntax": Unable to find syntax file for scope "source.less"
Error loading embed in syntax file "HTML (Astro).sublime-syntax": Unable to find syntax file for scope "source.sass"
Error loading embed in syntax file "HTML (Astro).sublime-syntax": Unable to find syntax file for scope "source.scss"
Error loading embed in syntax file "HTML (Astro).sublime-syntax": Unable to find syntax file for scope "source.stylus"

Local syntax tests succeed however, if no syntax related details are asserted.

Actual Behavior

But syntax-test-action fails, because it handles those error messages as syntax errors.

Expected Behavior

syntax-test-action should ignore "Error loading embed in syntax" messages and let CI run succeed in case no real syntax errors are detected.

[FichteFoll]

Currently, it's simply executing the test binary and using its output as well as the exit code. Ignoring some error cases would be possible but also require knowledge of all the other error codes because their presence still needs to cause failure.

[deathaxe]

Fixed by #19