chore(docker): wire all workflows to single-source version ARGs

The Dockerfile already centralizes all version pins into top-level ARGs
(GO_VERSION, ALPINE_IMAGE, CROWDSEC_VERSION, EXPR_LANG_VERSION, XNET_VERSION).
This change closes the remaining gaps so those ARGs are the single source of
truth end-to-end:

- nightly-build.yml now resolves the Alpine image digest at build time and
  passes ALPINE_IMAGE as a build-arg, matching the docker-build.yml pattern.
  Previously, nightly images were built with the Dockerfile ARG default and
  without a pinned digest, making runtime Alpine differ from docker-build.yml.

- six CI workflows (quality-checks, codecov-upload, benchmark, e2e-tests-split,
  release-goreleaser, codeql) declared a GO_VERSION env var but their setup-go
  steps ignored it and hardcoded the version string directly. They now reference
  ${{ env.GO_VERSION }}, so Renovate only needs to update one value per file
  and the env var actually serves its purpose.

- codeql.yml had no GO_VERSION env var at all; one is now added alongside the
  existing GOTOOLCHAIN: auto entry.

When Renovate bumps Go, it updates the env var at the top of each workflow and
the Dockerfile ARG — zero manual hunting required.

.github/workflows/nightly-build.yml

@@ -167,6 +167,14 @@ jobs:
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@4d04d5d9486b7bd6fa91e7baf45bbb4f8b9deedd  # v4.0.0
 
+      - name: Resolve Alpine base image digest
+        id: alpine
+        run: |
+          ALPINE_TAG=$(grep -m1 'ARG ALPINE_IMAGE=' Dockerfile | sed 's/ARG ALPINE_IMAGE=alpine://' | cut -d'@' -f1)
+          docker pull "alpine:${ALPINE_TAG}"
+          DIGEST=$(docker inspect --format='{{index .RepoDigests 0}}' "alpine:${ALPINE_TAG}")
+          echo "image=$DIGEST" >> "$GITHUB_OUTPUT"
+
       - name: Log in to GitHub Container Registry
         uses: docker/login-action@b45d80f862d83dbcd57f89517bcf500b2ab88fb2  # v4.0.0
         with:
@@ -210,6 +218,7 @@ jobs:
             VERSION=nightly-${{ github.sha }}
             VCS_REF=${{ github.sha }}
             BUILD_DATE=${{ github.event.repository.pushed_at }}
+            ALPINE_IMAGE=${{ steps.alpine.outputs.image }}
           cache-from: type=gha
           cache-to: type=gha,mode=max
           provenance: true