ci/cd: fix IPv6 timeouts with force-ipv4 action

This commit introduces the `force-ipv4` GitHub action to address
connectivity issues caused by the lack of IPv6 support in GitHub
runners. Details:
- actions/runner#3138
- actions/runner-images#668

This change solves connection problems when Node's `fetch` API fails due
to `UND_ERR_CONNECT_TIMEOUT` errors. Details:
- actions/runner-images#9540
- actions/runner#3213

This action disables IPv6 at the system level, ensuring all outging
requests use IPv4. Resolving connectivity issues when running external
URL checks and Docker build checks.

This solution is a temporary workaround until GitHub runners support
IPv6 or Node `fetch` API has a working solution such as Happy Eyeball.
Detais:
- nodejs/node#41625
- nodejs/undici#1531

.github/workflows/checks.build.yaml

@@ -95,6 +95,9 @@ jobs:
       -
         name: Run Docker image on port 8080
         run: docker run -d -p 8080:80 --rm --name privacy.sexy undergroundwires/privacy.sexy:latest
+      -
+        name: Enforce IPv4 Connectivity # Used due to GitHub runners' lack of IPv6 support, preventing request timeouts.
+        uses: ./.github/actions/force-ipv4
       -
         name: Check server is up and returns HTTP 200
         run: >-