ref(codecov): add 0.2% failure threshold to codecov (#1192)

This way, changes that drop coverage by less than a fifth of a percent will still pass. Anything
more than that should be looked at more closely by the reviewer for more potential places to cover
with tests.

Author: Matthew Fisher

codecov.yml

@@ -3,4 +3,7 @@ comment:
   layout: header, diff
 coverage:
   status:
+    project:
+      default:
+        threshold: 0.2
     changes: false