Ignore patch codecov as long as total coverage is within 1% of base

In some PRs, codecov gets mad that the coverage of the patch itself
is lower than the base. In most cases, we largely don't want a Big
Red X, at least as long as the total coverage has not gone down
substantially.

codecov.yml

@@ -3,6 +3,11 @@ coverage:
     project:
       default:
         target: auto
-        threshold: 2%
+        threshold: 1%
         base: auto
         informational: false
+    patch:
+      default:
+        target: auto
+        threshold: 100%
+        base: auto