ci(github): add GitHub validation workflow

Add a GitHub validation workflow that runs tests across supported Go
versions on every push to `main` branch as well as on every push to an
open PR.

.github/workflows/validation.yaml

@@ -0,0 +1,29 @@
+name: Validation
+
+on:
+  push:
+    branches: [ "main" ]
+  pull_request:
+    branches: [ "main" ]
+
+jobs:
+
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        go-version: [ '1.18', '1.19', '1.20', '1.21', '1.22' ]
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Go
+        uses: actions/setup-go@v5
+        with:
+          go-version: ${{ matrix.go-version }}
+
+      - name: Download dependencies
+        run: go mod download -x
+
+      - name: Test
+        run: go test -v ./...

go.sum

@@ -1,12 +1,9 @@
 github.com/alecthomas/assert/v2 v2.6.0 h1:o3WJwILtexrEUk3cUVal3oiQY2tfgr/FHWiz/v2n4FU=
-github.com/alecthomas/assert/v2 v2.6.0/go.mod h1:Bze95FyfUr7x34QZrjL+XP+0qgp/zg8yS+TtBj1WA3k=
 github.com/alecthomas/chroma/v2 v2.13.0 h1:VP72+99Fb2zEcYM0MeaWJmV+xQvz5v5cxRHd+ooU1lI=
 github.com/alecthomas/chroma/v2 v2.13.0/go.mod h1:BUGjjsD+ndS6eX37YgTchSEG+Jg9Jv1GiZs9sqPqztk=
 github.com/alecthomas/repr v0.4.0 h1:GhI2A8MACjfegCPVq9f1FLvIBS+DrQ2KQBFZP1iFzXc=
-github.com/alecthomas/repr v0.4.0/go.mod h1:Fr0507jx4eOXV7AlPV6AVZLYrLIuIeSOWtW57eE/O/4=
 github.com/dlclark/regexp2 v1.11.0 h1:G/nrcoOa7ZXlpoa/91N3X7mM3r8eIlMBBJZvsz/mxKI=
 github.com/dlclark/regexp2 v1.11.0/go.mod h1:DHkYz0B9wPfa6wondMfaivmHpzrQ3v9q8cnmRbL6yW8=
 github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
 github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
 github.com/hexops/gotextdiff v1.0.3 h1:gitA9+qJrrTCsiCl7+kh75nPqQt1cx4ZkudSTLoUqJM=
-github.com/hexops/gotextdiff v1.0.3/go.mod h1:pSWU5MAI3yDq+fZBTazCSJysOMbxWL1BSow5/V2vxeg=