Fix incorrect path in action.yml (#44)

## Problem

I accidentally pointed towards the action file itself, rather than its
dir.

## Solution

Point to its dir in the relative path (`./.github/actions/setup`, not
`./.github/actions/setup/action.yml`).

## Type of Change

- [x] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- [ ] This change requires a documentation update
- [ ] Infrastructure change (CI configs, etc)
- [ ] Non-code change (docs, etc)
- [ ] None of the above: (explain here)

.github/workflows/build-and-publish-docs.yml

@@ -15,7 +15,7 @@ jobs:
         uses: actions/checkout@v4
 
       - name: Setup Go
-        uses: ./.github/actions/setup/action.yml
+        uses: ./.github/actions/setup
 
       - name: Generate Go documentation
         uses: ./.github/actions/build-docs