ci: run make test during workflow

Tests for examples exist and are run as part of the Makefile test
target, however they were not being run as part of the CI. This commit
fixes it by adding a new step in the test workflow which runs said
target.

Related to go-git#912.

k

.github/workflows/test.yml

@@ -32,5 +32,10 @@ jobs:
         git config --global user.email "gha@example.com"
         git config --global user.name "GitHub Actions"
 
-    - name: Test
+    - name: Test Coverage
       run: make test-coverage
+
+    - name: Test
+      env:
+        EXAMPLES_DIR: _examples
+      run: make test