GitHub action to update vendor files

[smacker]

The same as #59 with the following changes:

• remove commit that changes lua grammar
• remove empty workflow
• run tests before committing changes

[smacker]

This job will only update grammars that point to master.
We probably want to modify it to automatically bump grammar pinned versions too.

Example run of the workflow: https://github.com/smacker/go-tree-sitter/runs/5120032143?check_suite_focus=true

[NickyBoy89]

Looks good! Thank you for all the help with this @smacker