ci(actions): pin prod-test action image (#43748)

## Bug

Test(Production) CI fails with error

```
Package libicu66 is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'ttf-unifont' has no installation candidate
E: Package 'ttf-ubuntu-font-family' has no installation candidate
E: Unable to locate package libenchant1c2a
E: Package 'libicu66' has no installation candidate
E: Unable to locate package libvpx6
E: Unable to locate package libwebp6
Failed to install browser dependencies
```

This is due to new release for the runner image (actions/runner-images#6399) now sets ubuntu 22.04 as latest, but playwright have release to support it (microsoft/playwright#13738) but @replayio/playwright seems not picked it up yet (https://github.com/replayio/replay-cli/blob/main/packages/playwright/package.json#L23) 

PR tries to pin to known working image (20.04) until dependencies can support new image gracefully.

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have a helpful link attached, see [`contributing.md`](https://github.com/vercel/next.js/blob/canary/contributing.md)

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] [e2e](https://github.com/vercel/next.js/blob/canary/contributing/core/testing.md#writing-tests-for-nextjs) tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have a helpful link attached, see [`contributing.md`](https://github.com/vercel/next.js/blob/canary/contributing.md)

## Documentation / Examples

- [ ] Make sure the linting passes by running `pnpm build && pnpm lint`
- [ ] The "examples guidelines" are followed from [our contributing doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)

.github/workflows/build_test_deploy.yml

@@ -617,7 +617,7 @@ jobs:
 
   testFirefox:
     name: Test Firefox (production)
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     needs: [build, build-native-test]
     timeout-minutes: 10
     env:
@@ -642,7 +642,7 @@ jobs:
 
   testSafari:
     name: Test Safari (production)
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     needs: [build, build-native-test]
     timeout-minutes: 15
     env:
@@ -719,7 +719,7 @@ jobs:
 
   testFirefoxNode18:
     name: Test Firefox Node.js 18
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     needs: [build, testFirefox, build-native-test]
     timeout-minutes: 10
     env:
@@ -970,7 +970,7 @@ jobs:
 
   test-wasm:
     name: Test the wasm build
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     timeout-minutes: 15
     needs: [build, build-native-test, build-wasm-dev]