Fix CI versions for incompatible Compose

- Docker Compose 2.24 broke behaviour we rely on for merging .env files. Versions since 2.27.1 restore this funcitonality: docker/compose#11824

.github/workflows/docker.yml

@@ -19,7 +19,7 @@ env:
 jobs:
   # builds all docker images in parallel
   build-docker:
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-22.04
 
     strategy:
       matrix:
@@ -200,7 +200,7 @@ jobs:
           retention-days: 1
 
   docs:
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-22.04
     needs: [build-docker]
     steps:
       - name: Branch deployment docs
@@ -275,7 +275,7 @@ jobs:
           sudo apt-get update
 
           # upgrade Docker
-          sudo apt install --upgrade docker-ce
+          sudo apt install --upgrade docker-ce docker-compose-plugin
 
       - name: Enable ip6tables in Docker
         run: |
@@ -360,7 +360,7 @@ jobs:
   lintcheck:
     name: lint/check
     needs: [build-docker]
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-22.04
 
     env:
       # used in `docker-compose.yml` files to determine version of images to pull
@@ -397,7 +397,7 @@ jobs:
 
   test:
     needs: [build-docker]
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-22.04
 
     env:
       # used in `docker-compose.yml` files to determine version of images to pull
@@ -450,7 +450,7 @@ jobs:
 
   development-environment-test:
     needs: [build-docker]
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-22.04
 
     env:
       # used in `docker-compose.yml` files to determine version of images to pull
@@ -562,7 +562,7 @@ jobs:
           sudo apt-get update
 
           # upgrade Docker
-          sudo apt install --upgrade docker-ce
+          sudo apt install --upgrade docker-ce docker-compose-plugin
 
       - name: Enable ip6tables in Docker
         run: |