ci: fix gated x86 job staying 'queued' instead of 'skipped'

After v0.3.1 published successfully, run 524 stayed in 'queued' status
overall even though all 5 jobs that actually ran completed at success.
Cause: the gated build-iso-amd64 job is `if: false` with
`runs-on: amd64-linux`. No runner matches `amd64-linux`, so Gitea
queued the job indefinitely waiting for one. The `if:` expression
is only evaluated when a runner actually picks up the job, so the
skip never fires.

Switch the runs-on to `ubuntu-latest` (which our Odroid claims). The
runner picks the job up, evaluates `if: false`, marks it `skipped`,
and the run as a whole concludes properly.

Comment block updated to flag the two lines to flip when a real
amd64-linux runner is registered.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitea/workflows/release.yaml

@@ -76,14 +76,15 @@ jobs:
 
   build-iso-amd64:
     name: Build x86_64 ISO + disk image
-    # Routes to a runner with the `amd64-linux` label. As of v0.3.x no such
-    # runner exists in this Gitea instance — the only runner is the Odroid
-    # which is arm64 and would fail apt-installing grub-efi-amd64-bin /
-    # syslinux because those packages aren't in the arm64 ports repo. The
-    # job stays in the workflow (so it auto-runs once an amd64 runner is
-    # registered) but is gated and the release job continues without it.
-    if: false   # remove this line once an amd64-linux runner is registered
-    runs-on: amd64-linux
+    # Gated until an amd64-linux runner is registered. We use `runs-on:
+    # ubuntu-latest` (which the Odroid claims) so SOME runner picks the job
+    # up and evaluates `if: false`, marking it `skipped` instead of leaving
+    # it `queued` forever — the latter holds the overall run in `queued`
+    # state even when every load-bearing job is complete. When we get an
+    # amd64 runner, flip `if: false` to `false` -> `true` (and flip the
+    # `runs-on:` back to `amd64-linux`).
+    if: false
+    runs-on: ubuntu-latest
     needs: build-binaries
     steps:
       - uses: actions/checkout@v4