ci: remove stylua action & update PR template

.github/pull_request_template.md

@@ -1,5 +1,5 @@
 ## Checklist
 - [ ] Used only camelCase variable names.
 - [ ] If functionality is added or modified, also made respective changes to the
-  readme.
+  `README.md` (the `.txt` file is auto-generated and does not need to be modified).
-- [ ] Used conventional commits keywords.
+- [ ] If a non-trivial PR, formatting via `stylua`.

.github/workflows/stylua.yml

@@ -1,16 +0,0 @@
-name: Linting and style checking
-
-on: [pull_request]
-
-jobs:
-  stylua:
-    name: stylua
-    runs-on: ubuntu-20.04
-    steps:
-      - uses: actions/checkout@v3
-      - uses: JohnnyMorganz/stylua-action@v2
-        with:
-          token: ${{ secrets.GITHUB_TOKEN }}
-          version: latest
-          # CLI arguments
-          args: --color always --check lua/