ci: Make CI fail if code isn't formatted properly (#61)

For:
#60

---------

Co-authored-by: sanchegm <[email protected]>

Author: liammulh

.github/workflows/check.yml

@@ -32,7 +32,7 @@ jobs:
       - name: install dependencies
         run: pipenv sync --dev # Installs all deps, including dev deps, from Pipfile.lock.
       - name: format
-        run: pipenv run invoke fmt
+        run: pipenv run invoke fmtcheck
       - name: lint
         run: pipenv run invoke lint
       - name: check types

tasks.py

@@ -35,6 +35,12 @@ def fmt(c):
     c.run("mdformat doc")
 
 
+@task
+def fmtcheck(c):
+    """Checks if the code is formatted properly."""
+    c.run("black --check .")
+
+
 @task
 def lint(c):
     """Run the linter."""