ci: run the github wait job on its own runner label

The github job only polls Gitea for GitHub's commit status, but it holds a
runner slot for as long as the GitHub build takes -- the better part of an
hour for a cold build. On the shared build runners a handful of those
could take every slot and stall real work, so it now runs on the `wait`
label: a runner of its own, with many slots, no docker socket and a small
CPU and memory cap.

.gitea/workflows/ci.yml

@@ -116,7 +116,9 @@ jobs:
   # timeout this fails, which is the cue to unset BUILD_ON.
   github:
     if: ${{ vars.BUILD_ON == 'github' }}
-    runs-on: light
+    # Its own runner label with plenty of slots: this job only polls, but holds a slot
+    # for as long as the GitHub build takes, and must not starve the build runners.
+    runs-on: wait
     timeout-minutes: 150
     container:
       image: python:3.13-slim@sha256:8d9d0b8bcf6506481eae4907c18f5e3e7902e629f5f6d684f9e7c32e85e3ddf0 # 3.13-slim

.gitea/workflows/publish.yml

@@ -178,7 +178,9 @@ jobs:
   # its answer. Fails after the timeout if no answer comes.
   github:
     if: ${{ vars.BUILD_ON == 'github' }}
-    runs-on: light
+    # Its own runner label with plenty of slots: this job only polls, but holds a slot
+    # for as long as the GitHub build takes, and must not starve the build runners.
+    runs-on: wait
     timeout-minutes: 240
     container:
       image: python:3.13-slim@sha256:8d9d0b8bcf6506481eae4907c18f5e3e7902e629f5f6d684f9e7c32e85e3ddf0 # 3.13-slim