chore: suggest using ubuntu-slim as runtime container

Also add a e2e test to verify that it works as intended.

PR: #195

Author: jbergstroem

.github/workflows/test-e2e.yml

@@ -22,6 +22,17 @@ jobs:
         with:
           dockerfile: test/fixtures/Dockerfile-valid
 
+  gh-action-default-slim:
+    name: Action validates Dockerfiles using the `ubuntu-slim` container
+    runs-on: ubuntu-slim
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          persist-credentials: false
+      - uses: ./
+        with:
+          dockerfile: test/fixtures/Dockerfile-valid
+
   gh-action-version:
     name: Action supports custom version
     runs-on: ubuntu-24.04

README.md

@@ -12,7 +12,7 @@ on: pull_request
 
 jobs:
   hadolint:
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-slim
     name: Hadolint
     steps:
       - uses: actions/checkout@v6

USAGE.md

@@ -15,7 +15,7 @@ on: pull_request
 
 jobs:
   hadolint:
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-slim
     name: Hadolint
     steps:
       - uses: actions/checkout@v6
@@ -50,7 +50,7 @@ on:
 
 jobs:
   hadolint:
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-slim
     name: Hadolint
     steps:
       - uses: actions/checkout@v6
@@ -78,7 +78,7 @@ on: pull_request
 
 jobs:
   hadolint:
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-slim
     name: Hadolint"
     steps:
       - uses: actions/checkout@v6
@@ -101,7 +101,7 @@ on: pull_request
 
 jobs:
   hadolint:
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-slim
     name: Hadolint
     steps:
       - uses: actions/checkout@v6
@@ -141,7 +141,7 @@ permissions:
 
 jobs:
   hadolint:
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-slim
     name: Hadolint
     steps:
       - uses: actions/checkout@v6