feat(go-release): add optional runner input (default ubuntu-latest)

Lets a caller run the release jobs on a self-hosted runner via with.runner,
e.g. runner: self-hosted. Defaults to ubuntu-latest so existing consumers are
unaffected.

.github/workflows/go-release.yaml

@@ -33,6 +33,11 @@ on:
         required: false
         type: boolean
         default: false
+      runner:
+        description: "Runner label(s) for the release jobs. Defaults to ubuntu-latest; set to a self-hosted label (e.g. self-hosted) to run on your own runner."
+        required: false
+        type: string
+        default: "ubuntu-latest"
     outputs:
       version:
         description: "The calculated version (without v prefix)"
@@ -44,7 +49,7 @@ on:
 jobs:
   test:
     name: Test
-    runs-on: ubuntu-latest
+    runs-on: ${{ inputs.runner }}
     steps:
       - name: Checkout
         uses: actions/checkout@v6
@@ -67,7 +72,7 @@ jobs:
   version:
     name: Calculate Version
     needs: test
-    runs-on: ubuntu-latest
+    runs-on: ${{ inputs.runner }}
     outputs:
       version: ${{ steps.semver.outputs.version }}
       version_tag: ${{ steps.semver.outputs.version_tag }}
@@ -96,7 +101,7 @@ jobs:
     name: Release
     needs: version
     if: needs.version.outputs.version_tag != ''
-    runs-on: ubuntu-latest
+    runs-on: ${{ inputs.runner }}
     permissions:
       contents: write
       packages: write