Remove independent build and cache job

Our caching strategy is to cached across CI jobs with the focus on
caching the layers in the Docker image.

As each job has to build the image from (using the cache) regardless, we
think we can get rid of the independent build and cache job and let the
caching happen as we run each job.

The only way to see if this pays off is to merge the changes and run
another CI workflow to see how much caching we get.

.github/actions/continuous-integration/load-cache/action.yml

@@ -17,3 +17,4 @@ runs:
         load: true
         tags: app_test:latest
         cache-from: type=gha
+        cache-to: type=gha,mode=min

.github/workflows/continuous-integration.yml

@@ -10,38 +10,15 @@ on:
       - develop
 
 jobs:
-  build-and-cache:
-    name: Build and cache image
-    runs-on: ubuntu-latest
-    steps:
-      -
-        name: Checkout
-        uses: actions/checkout@v4
-      -
-        name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@v3
-      -
-        name: Build and cache image
-        uses: docker/build-push-action@v6
-        with:
-          context: .
-          file: ./Dockerfile
-          build-args: RAILS_ENV=test
-          push: false
-          tags: app_test:latest
-          cache-from: type=gha
-          cache-to: type=gha,mode=min
-
   lint-and-format:
     name: Lint and format application
     runs-on: ubuntu-latest
-    needs: build-and-cache
     steps:
       -
         name: Checkout
         uses: actions/checkout@v4
       -
-        name: Load cache
+        name: Build and cache
         uses: ./.github/actions/continuous-integration/load-cache
       -
         name: Run linters and formatters
@@ -54,13 +31,12 @@ jobs:
   static-analysis:
     name: Static analysis
     runs-on: ubuntu-latest
-    needs: build-and-cache
     steps:
       -
         name: Checkout
         uses: actions/checkout@v4
       -
-        name: Load cache
+        name: Build and cache
         uses: ./.github/actions/continuous-integration/load-cache
       -
         name: Run Brakeman
@@ -70,13 +46,12 @@ jobs:
   specs:
     name: Specs and coverage
     runs-on: ubuntu-latest
-    needs: build-and-cache
     steps:
       -
         name: Checkout
         uses: actions/checkout@v4
       -
-        name: Load cache
+        name: Build and cache
         uses: ./.github/actions/continuous-integration/load-cache
       -
         name: Run RSpec and Simplecov