root: set codecov after_n_builds and threshold (#5137)

Signed-off-by: Jens Langhammer <jens@goauthentik.io>

.github/codecov.yml

@@ -1,3 +1,10 @@
 coverage:
-  precision: 2
+  status:
-  round: up
+    project:
+      default:
+        target: auto
+        # adjust accordingly based on how flaky your tests are
+        # this allows a 1% drop from the previous base commit coverage
+        threshold: 1%
+  notify:
+    after_n_builds: 3