Replace buildenv image with a container reference

.gitea/workflows/build.yml

@@ -7,13 +7,13 @@ on:
 
 jobs:
   audit:
-    runs-on: buildenv
+    container: buildenv:5
     steps:
       - uses: actions/checkout@v4
       - run: hlint src lib test
 
   test:
-    runs-on: buildenv
+    container: buildenv:5
     steps:
       - name: Set up environment
         run: |
@@ -25,7 +25,7 @@ jobs:
       - run: cabal test --test-show-details=streaming
 
   release:
-    runs-on: buildenv
+    container: buildenv:5
     steps:
       - name: Set up environment
         run: |

.gitea/workflows/deploy.yaml

@@ -7,7 +7,7 @@ on:
 
 jobs:
   release:
-    runs-on: buildenv
+    container: buildenv:5
     steps:
       - name: Set up environment
         run: |