test: speed up tests (#1181)

Parallelize isolated workflow tests, consolidate redundant fixtures, and replace fixed waits with deterministic synchronization. Keep the readable curl service probe and use `getent` for hostname resolution.

Measured on the same machine with `make test`:

1. Wall time: 170.50s to 136.12s, down 34.38s or 20.2%.
1. `act/runner`: 138.417s to 124.291s, down 14.126s or 10.2%.
1. `act/runner` coverage: unchanged at 85.2%.
1. `TestDockerExecAbort`: 2.514s to 0.012s package time.

Stability checks:

1. Cancellation and deadline tests: 100 race-enabled repetitions.
1. Host runner suite: 10 race-enabled repetitions.
1. Changed Docker fixtures: 3 consecutive repetitions.

Full race suite, Go and Windows lint, source checks, and security scan pass.

Assisted-by: Codex:GPT-5
Reviewed-on: https://gitea.com/gitea/runner/pulls/1181
Reviewed-by: bircni <bircni@icloud.com>
Co-authored-by: silverwind <me@silverwind.io>

act/runner/testdata/steps-context/conclusion/push.yml

@@ -1,14 +0,0 @@
-name: conclusion
-on: push
-
-jobs:
-  check:
-    runs-on: ubuntu-latest
-    steps:
-      - id: first
-        run: exit 0
-      - id: second
-        continue-on-error: true
-        run: exit 1
-      - run: echo '${{ steps.first.conclusion }}' | grep 'success'
-      - run: echo '${{ steps.second.conclusion }}' | grep 'success'

act/runner/testdata/steps-context/outcome/push.yml

@@ -1,14 +0,0 @@
-name: outcome
-on: push
-
-jobs:
-  check:
-    runs-on: ubuntu-latest
-    steps:
-      - id: first
-        run: exit 0
-      - id: second
-        continue-on-error: true
-        run: exit 1
-      - run: echo '${{ steps.first.outcome }}' | grep 'success'
-      - run: echo '${{ steps.second.outcome }}' | grep 'failure'

act/runner/testdata/steps-context/push.yml

@@ -0,0 +1,17 @@
+name: steps context
+on: push
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      - id: first
+        run: exit 0
+      - id: second
+        continue-on-error: true
+        run: exit 1
+      - run: |
+          test '${{ steps.first.conclusion }}' = success
+          test '${{ steps.second.conclusion }}' = success
+          test '${{ steps.first.outcome }}' = success
+          test '${{ steps.second.outcome }}' = failure