ci: use devcontainer build script in CI. Also re-tag it as 'gas' instead of 'gas/ci' (which should be redundant)

.gitea/workflows/CI.yaml

@@ -3,14 +3,14 @@ name: CI
 on: [push]
 
 jobs:
-  # These steps build the `gas/ci` docker image.
+  # These steps build the `gas` docker image.
   # There's a tricky bootstrapping problem here.  We'll try to cheat first, and if that doesn't
   # work, then we'll do a full bootstrapping build starting from Alpine and installing `gocheckout`
   # first thing.
   build-docker:
     continue-on-error: true
     container:
-      image: gas/ci
+      image: gas
       volumes:
         - woodpecker-gocache:/go-cache-volume
       env:
@@ -23,7 +23,7 @@ jobs:
         run: gocheckout
 
       - name: build CI container
-        run: docker build -t gas/ci ops/devcontainer
+        run: ops/devcontainer/build.sh
 
   # Fallback: full bootstrap build.  This one is quite slow.
   build-docker-bootstrap:
@@ -51,13 +51,13 @@ jobs:
         run: apk add docker
 
       - name: build CI container
-        run: docker build -t gas/ci ops/devcontainer
+        run: ops/devcontainer/build.sh
 
   release-test:
     needs: build-docker-bootstrap
     if: "!failure()"
     container:
-      image: gas/ci
+      image: gas
       volumes:
         - woodpecker-gocache:/go-cache-volume
       env: