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/renovate.json

@@ -69,12 +69,45 @@
       "description": "Track Alpine base image digest in Dockerfile for security updates",
       "managerFilePatterns": ["/^Dockerfile$/"],
       "matchStrings": [
-        "#\\s*renovate:\\s*datasource=docker\\s+depName=alpine.*\\nARG CADDY_IMAGE=alpine:(?<currentValue>[^\\s@]+@sha256:[a-f0-9]+)"
+        "#\\s*renovate:\\s*datasource=docker\\s+depName=alpine.*\\nARG ALPINE_IMAGE=alpine:(?<currentValue>[^@\\s]+)@(?<currentDigest>sha256:[a-f0-9]+)"
       ],
       "depNameTemplate": "alpine",
       "datasourceTemplate": "docker",
       "versioningTemplate": "docker"
     },
+    {
+      "customType": "regex",
+      "description": "Track Go toolchain version ARG in Dockerfile",
+      "managerFilePatterns": ["/^Dockerfile$/"],
+      "matchStrings": [
+        "#\\s*renovate:\\s*datasource=docker\\s+depName=golang.*\\nARG GO_VERSION=(?<currentValue>[^\\s]+)"
+      ],
+      "depNameTemplate": "golang",
+      "datasourceTemplate": "docker",
+      "versioningTemplate": "docker"
+    },
+    {
+      "customType": "regex",
+      "description": "Track expr-lang version ARG in Dockerfile",
+      "managerFilePatterns": ["/^Dockerfile$/"],
+      "matchStrings": [
+        "#\\s*renovate:\\s*datasource=go\\s+depName=github\\.com/expr-lang/expr.*\\nARG EXPR_LANG_VERSION=(?<currentValue>[^\\s]+)"
+      ],
+      "depNameTemplate": "github.com/expr-lang/expr",
+      "datasourceTemplate": "go",
+      "versioningTemplate": "semver"
+    },
+    {
+      "customType": "regex",
+      "description": "Track golang.org/x/net version ARG in Dockerfile",
+      "managerFilePatterns": ["/^Dockerfile$/"],
+      "matchStrings": [
+        "#\\s*renovate:\\s*datasource=go\\s+depName=golang\\.org/x/net.*\\nARG XNET_VERSION=(?<currentValue>[^\\s]+)"
+      ],
+      "depNameTemplate": "golang.org/x/net",
+      "datasourceTemplate": "go",
+      "versioningTemplate": "semver"
+    },
     {
       "customType": "regex",
       "description": "Track Delve version in Dockerfile",