CI: revert to container-based test job; correct the NetworkPolicy claim

Host-mode (previous commit) fails earlier and differently: "go: command not
found" -- the runner host has no Go, so that path is dead.

Checked Ryuvia/charts' act-runner/templates/networkpolicy.yaml directly
rather than assuming: it's the only NetworkPolicy in the cluster, and it is
explicitly deny-ingress only -- its own comment states egress is
deliberately untouched, "CI pulls from registries and package indexes that
are not enumerable here" (issue #128). So my earlier claim that this needs
"allowlisting github.com on the runner's NetworkPolicy" was wrong: there is
no in-repo egress rule governing this at all. Whatever blocks github.com
from the dind bridge is outside anything Ryuvia/charts or Ryuvia/k8s
expresses in a Kubernetes object -- back to container-based (matching every
other Go job in this org) as the known-good shape, with `make test` left
red on the envtest fetch until that's actually found.

.gitea/workflows/ci.yaml

@@ -31,22 +31,34 @@ jobs:
   # and a green working copy mean the same thing by construction. `test` also drives
   # controller-gen/setup-envtest (via the Makefile's own `manifests generate ... test`
   # chain), which fetches the envtest kube-apiserver/etcd binaries from GitHub Releases
-  # (setup-envtest v0.25's only source -- the legacy GCS kubebuilder-tools bucket
-  # 403s now, confirmed 2026-09-30, no fallback there for k8s 1.37).
+  # (setup-envtest v0.25's only source -- the legacy GCS kubebuilder-tools bucket 403s
+  # now for every version tried, confirmed 2026-09-30, no fallback there).
   #
-  # Confirmed the hard way: running this in `container: golang:1.26.6-bookworm` hits
-  # exactly the restriction terdut-server's ci.yaml already documents for
-  # get.helm.sh/github.com -- TLS handshake timeout reaching github.com from the dind
-  # bridge. No `container:` here, unlike every other Go job in this org's repos, on
-  # the same theory as terdut-server's `chart` job (which reaches get.helm.sh only by
-  # running on the host, not in a container) -- this is that same fix applied to a Go
-  # job for the first time, so it additionally assumes the runner host has Go
-  # available directly, which no prior workflow here has needed. If this goes red on
-  # "go: command not found" rather than the envtest fetch, that assumption was wrong
-  # and this needs the other fix instead (allowlist github.com's release CDN on the
-  # runner's NetworkPolicy, in Ryuvia/charts or Ryuvia/k8s).
+  # This currently fails in CI: TLS handshake timeout reaching github.com from inside
+  # this container, same symptom terdut-server's ci.yaml already documents for
+  # get.helm.sh/github.com. Two things ruled out already, so this isn't "add an
+  # allowlist entry":
+  #   - Ryuvia/charts' act-runner/templates/networkpolicy.yaml is the only
+  #     NetworkPolicy in the cluster, and it is deny-ingress only, by explicit design
+  #     ("egress is deliberately untouched... CI pulls from registries and package
+  #     indexes that are not enumerable here" -- see its own comment, issue #128).
+  #     There is no in-repo egress rule to edit for this.
+  #   - Running this job on the bare runner host instead of in a container (tried and
+  #     reverted, same as terdut-server's `chart` job does for get.helm.sh) fails
+  #     earlier and differently: "go: command not found" -- the host has no Go.
+  # So whatever blocks github.com from the dind bridge sits outside anything this
+  # workspace's repos configure -- a firewall/DNS layer neither Ryuvia/charts nor
+  # Ryuvia/k8s expresses in Kubernetes objects. `make test` fails on the envtest fetch
+  # until that's found and fixed (or the binaries are vendored -- see ROADMAP.md/the
+  # PR discussion for why that was declined for now).
   test:
     runs-on: ubuntu-latest
+    container:
+      image: golang:1.26.6-bookworm
+      volumes:
+        - go-mod-cache:/go/pkg/mod
+        - go-build-cache:/root/.cache/go-build
+        - gobin-cache:/go/bin
 
     steps:
       - name: Checkout