Update Go version used in the CI using renovate (#3585)

This should always be the latest version of Go, but should also be
explicitly pinned at least at the minor level. Renovate can do this for
us, and the maintenance burden of merging the update PRs should be
minimal.

renovate.json

@@ -3,6 +3,18 @@
   "labels": ["dependencies"],
   "enabledManagers": ["regex"],
   "customManagers": [
+    {
+      "customType": "regex",
+      "description" : "Update Go versions used for building in the CI",
+      "datasourceTemplate": "golang-version",
+      "depNameTemplate": "go",
+      "fileMatch": [
+        "(^|/)\\.github/workflows/.+\\.ya?ml$"
+      ],
+      "matchStrings": [
+        "go-version: \"~(?<currentValue>.+)\""
+      ]
+    },
     {
       "customType": "regex",
       "description" : "Update tool versions in the Makefile",
@@ -15,6 +27,12 @@
     }
   ],
   "packageRules": [
+    {
+      "matchDatasources": ["golang-version"],
+      "matchManagers": ["regex"],
+      "matchFileNames": [".github/workflows/*.yaml", ".github/workflows/*.yml"],
+      "commitMessageTopic": "go version in CI"
+    },
     {
       "matchManagers": ["regex"],
       "matchFileNames": ["Makefile"],