Add codecov.yml configuration file (#85)

This commit adds an explicit Codecov configuration file to set up a
threshold for project and patch coverage regressions. This avoid
spurious detections in dependabot patches.

codecov.yml

@@ -0,0 +1,12 @@
+codecov:
+  require_ci_to_pass: true
+coverage:
+  status:
+    project:
+      default:
+        target: auto
+        threshold: 0.5%
+    patch:
+      default:
+        target: auto
+        threshold: 0.5%