Pin Go version

This is required in a couple situations:

- On GitHub Actions, to avoid running whatever version that comes with
  the 'golangci-lint' action and might break things.
- Locally, when using 'asdf', as the 'go.mod' support[1] is confusing
  and doesn't work flawlessly.

[1]: https://github.com/asdf-community/asdf-golang#version-selection

.github/workflows/qa.yml

@@ -7,6 +7,9 @@ jobs:
     runs-on: ubuntu-22.04
     steps:
       - uses: actions/checkout@v3
+      - uses: actions/setup-go@v3
+        with:
+          go-version-file: go.mod
       - name: Install dependencies
         run: |
           pip install yamllint==1.26.*

.go-version

@@ -0,0 +1 @@
+1.20