refactor(actions): simplify run-vociferate runtime flow

run-vociferate.code/action.yml

@@ -2,9 +2,6 @@ name: vociferate/run-vociferate-code
 description: Execute vociferate from the checked-out Go source.
 
 inputs:
-  source-root:
-    description: Action repository root containing the Go module.
-    required: true
   root:
     description: Repository root to pass to vociferate.
     required: true
@@ -49,10 +46,30 @@ outputs:
 runs:
   using: composite
   steps:
+    - name: Resolve source root
+      id: resolve-source
+      shell: bash
+      run: |
+        set -euo pipefail
+
+        source_root="$GITHUB_ACTION_PATH"
+        if [[ ! -f "$source_root/go.mod" ]]; then
+          source_root="$(realpath "$GITHUB_ACTION_PATH/..")"
+        fi
+
+        printf 'source_root=%s\n' "$source_root" >> "$GITHUB_OUTPUT"
+
+    - name: Setup Go
+      uses: actions/setup-go@v5
+      with:
+        go-version: '1.26.1'
+        cache: true
+        cache-dependency-path: ${{ steps.resolve-source.outputs.source_root }}/go.sum
+
     - name: Run source
       id: run
       shell: bash
-      working-directory: ${{ inputs.source-root }}
+      working-directory: ${{ steps.resolve-source.outputs.source_root }}
       env:
         ROOT: ${{ inputs.root }}
         VERSION_FILE: ${{ inputs.version-file }}