ci: adjust workflows to enable required checks

Auto-merging is a useful feature by github, but it requires required
checks which requires a few adjustments. The primary change is that
required checks can't use `paths` or `paths-ignore` as that risks not
running the job, and required checks must always be run.

A workaround for this is to introduce a dummy workflow which is used for
every path not used in the real workflow. That way the required job is
"always" run as far as github is concerned. The workaround is unweildly
so it's only useful to do it for costly workflows where the potential
benefits are big. If not it's better to simply remove any `paths` or
`paths-ignore` from a workflow instead.

.github/workflows/docs.yml

@@ -2,13 +2,6 @@ name: docs
 on:
   pull_request:
     types: [opened, synchronize, reopened, ready_for_review]
-    paths:
-      - 'src/nvim/api/*.[ch]'
-      - 'src/nvim/eval.lua'
-      - 'runtime/lua/**.lua'
-      - 'runtime/doc/**'
-      - 'scripts/gen_vimdoc.py'
-      - 'scripts/gen_help_html.lua'
 jobs:
   docs:
     runs-on: ubuntu-latest