fix: keep dry runs off the docker daemon and speed up the tests (#1349)

Without a docker daemon six `act/runner` tests failed instead of passing. A dry run still created and removed job networks, the job teardown dropped the dry-run flag along with every other context value, and the container mocks asked the daemon for the runner arch.

This also speeds up the tests and CI without dropping assertions. Most of the time went to git and docker round trips, which are now pinned, batched or coalesced, and the dind and e2e steps cache or overlap more of their setup. On CI, `act/runner` went from 77s to 55s and `test-dind` from 108s to 55s. Locally, `act/runner` without docker went from 53s to 7s.

Split out of https://gitea.com/gitea/runner/pulls/1348, which adds Windows CI on top. The go cache changes moved to https://gitea.com/gitea/runner/pulls/1350.

Written by Claude Code.

---------

Co-authored-by: bircni <[email protected]>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1349
Reviewed-by: bircni <[email protected]>
Co-authored-by: silverwind <[email protected]>

.gitea/workflows/test.yml

@@ -22,17 +22,19 @@ jobs:
         run: mkdir -p "$DOCKER_CONFIG" && echo '{}' > "$DOCKER_CONFIG/config.json"
       # Pre-pull act/runner's two largest base images so a slow pull can't dominate `make test`;
       # the rest (alpine/ubuntu) pull on demand, absorbed by the make-test -timeout. The host
-      # daemon retains them between runs, so this is usually a fast manifest re-check.
+      # daemon retains them between runs, and their digest pins skip the registry when it has them.
       - name: pre-pull test images
         env:
           TEST_JOB_IMAGE: node:24-bookworm-slim@sha256:55fb5f5a527ea2c5c4a95f963e48ef90aa38c7b346054fdc8ee9957a2b55d205 # renovate: datasource=docker
           TEST_SERVICE_IMAGE: nginx:alpine@sha256:a3554c0d0b48177b1413c26e01f695334428020d9df01243fbae3e11cfd17417 # renovate: datasource=docker
         run: |
           for image in "$TEST_JOB_IMAGE" "$TEST_SERVICE_IMAGE"; do
-            for attempt in 1 2 3; do
-              docker pull "$image" && break
-              [ "$attempt" = 3 ] || sleep 5
-            done
+            if [ "$(docker image inspect --format '{{.Os}}/{{.Architecture}}' "$image" 2>/dev/null)" != linux/amd64 ]; then
+              for attempt in 1 2 3; do
+                docker pull "$image" && break
+                [ "$attempt" = 3 ] || sleep 5
+              done
+            fi
             docker tag "$image" "${image%@*}"
           done
       - name: lint