chore: add Artemy as CODEOWNER for CI and tests (#32)

ensures he gets cc'd/can review any changes


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Chores**
* Updated repository ownership rules: preserved default global owners
for most files while introducing dedicated per-directory owners for CI
and test areas and removing one previously listed global owner.
  * No changes to user-facing functionality or public APIs.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: nathan-weinberg

.github/CODEOWNERS

@@ -2,4 +2,8 @@
 
 # These owners will be the default owners for everything in
 # the repo. Unless a later match takes precedence,
-* @cdoern @derekhiggins @Elbehery @leseb @mfleader @nathan-weinberg @rhdedgar @rhuss @skamenan7 @VaishnaviHire
+* @cdoern @derekhiggins @Elbehery @leseb @nathan-weinberg @rhdedgar @rhuss @skamenan7 @VaishnaviHire
+
+# These owners will own only CI and testing related infrastructure
+.github/ @Artemon-line @kami619
+tests/ @Artemon-line @kami619