Update CODEOWNERS

Make @iirina codeowners of only the coverage parts of tools/test.

Closes #6279.

PiperOrigin-RevId: 215215651
diff --git a/CODEOWNERS b/CODEOWNERS
index 640affa..d96200f 100644
--- a/CODEOWNERS
+++ b/CODEOWNERS
@@ -84,4 +84,6 @@
 /src/main/java/com/google/devtools/build/lib/syntax/ @brandjon @c-parsons @dkelmer @dslomov @laurentlb @vladmos
 
 /tools/coverage/ @iirina
-/tools/test/ @iirina
+/tools/test/collect_coverage.sh @iirina
+/tools/test/collect_cc_coverage.sh @iirina
+/tools/test/CoverageOutputGenerator/ @iirina