ci(codecov): adjust threshold and noise settings (#615)

Fixes https://github.com/ratatui-org/ratatui/issues/612

codecov.yml

@@ -1,3 +1,14 @@
+coverage: # https://docs.codecov.com/docs/codecovyml-reference#coverage
+  precision: 1 # e.g. 89.1%
+  round: down
+  range: 85..100 # https://docs.codecov.com/docs/coverage-configuration#section-range
+  status: # https://docs.codecov.com/docs/commit-status
+    project:
+      default:
+        threshold: 1% # Avoid false negatives
 ignore:
   - "examples"
   - "benches"
+comment: # https://docs.codecov.com/docs/pull-request-comments
+  # make the comments less noisy
+  require_changes: true