ci: use GitHub-hosted ubuntu-latest runners (#34)

Public repos get free, unlimited standard GitHub-hosted runners. Move
self-hosted Linux CI jobs to ubuntu-latest: frees the home-lab servers,
runs PR code in throwaway isolated VMs (removing the fork-PR attack
surface), and costs nothing on public repos. The previous self-hosted
fork-guard is removed as it is no longer needed.

Co-authored-by: GeiserX <drumsergio@gmail.com>

Author: GeiserX

.github/workflows/docker-publish.yml

@@ -19,7 +19,7 @@ env:
 
 jobs:
   build-and-push:
-    runs-on: [self-hosted, Linux, X64]
+    runs-on: ubuntu-latest
     permissions:
       contents: read
       packages: write

.github/workflows/dockerhub-description.yml

@@ -8,7 +8,7 @@ on:
 
 jobs:
   update-description:
-    runs-on: [self-hosted, Linux, X64]
+    runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v6
 

.github/workflows/stale.yml

@@ -5,7 +5,7 @@ on:
 
 jobs:
   stale:
-    runs-on: [self-hosted, Linux, X64]
+    runs-on: ubuntu-latest
     steps:
       - uses: actions/stale@v10
         with:

.github/workflows/tests.yml

@@ -9,11 +9,7 @@ on:
 
 jobs:
   test:
-    runs-on: [self-hosted, Linux, X64]
-    # Do not run untrusted fork PR code on the self-hosted runner.
-    if: >-
-      github.event_name != 'pull_request' ||
-      github.event.pull_request.head.repo.full_name == github.repository
+    runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v6