There's a merged pull request on the void-packages repository

travis/changed_templates: filter by git itself
https://github.com/void-linux/void-packages/pull/22228

Description:
- Use plumbing git-diff-tree(1) instead of porcelain git-diff(1)
- Disable rename detection, gains some speed up and fix missing template
  with name-status Renamed and Copied.
- Use "--diff-filter" to filter by Git itself.
- Tell Git to only check 'srcpkgs/*/template', this glob will only look
  into template file inside direct sub-directory of srcpkgs
- With all of those options, we don't need a grep and a pipe

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@Gottox you're the author of original script, this will speed up the script a bit.
I'll merge this in 2020-05-30 if nobody complains.