CI: Only build if checks pass

.github/workflows/build.yml

@@ -8,10 +8,20 @@
 # and the Docker version on Docker Hub is super outdated.  Oh well, this is
 # faster anyway.
 
-name: Build and publish Docker image
+name: Run checks, build and publish Docker image
 on: [push]
 jobs:
-  build:
+  Check:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@master
+    - uses: actions/setup-python@master
+    - name: Install and run pre-commit
+      run: |
+        pip install pre-commit
+        pre-commit run -a -v
+  Build:
+    needs: check
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@master

.github/workflows/pre-commit.yml

@@ -1,12 +0,0 @@
-name: Check
-on: [push]
-jobs:
-  build:
-    runs-on: ubuntu-latest
-    steps:
-    - uses: actions/checkout@master
-    - uses: actions/setup-python@master
-    - name: Install and run pre-commit
-      run: |
-        pip install pre-commit
-        pre-commit run -a -v