codecov: add threshold values

Adds desired targets and threshold values for code coverage tests in
pull requests.

Removes custom code coverage range to fall back to codecov defaults.

.github/codecov.yml

@@ -2,9 +2,15 @@ codecov:
   require_ci_to_pass: yes
 
 coverage:
-  precision: 2
-  round: down
-  range: "80...100"
+  status:
+    patch:
+      default:
+        informational: true
+    project:
+      default:
+        base: auto
+        target: auto
+        threshold: 2%
 
 parsers:
   gcov: