chore(.github/CODEOWNERS): two new rules (#16921)

There is an attempt to order the rules from generic to specific.

.github/CODEOWNERS

@@ -1,13 +1,19 @@
 # By default, the mathlib maintainers own everything in the repo.
 # Later matches will take precedence over this match.
+
 # Disabled until we have better coverage by other patterns. Reenable in the future.
-# *	@leanprover-community/mathlib-maintainers
+# *        @leanprover-community/mathlib-maintainers
+
+src/category_theory/    @leanprover-community/mathlib-CT
 
-src/tactic/		@leanprover-community/mathlib-meta
+src/measure_theory/     @leanprover-community/mathlib-meas
 
-src/category_theory/	@leanprover-community/mathlib-CT
 src/algebraic_topology/ @leanprover-community/mathlib-CT # for now the category theory team can take care of this
 
 src/algebraic_geometry/ @leanprover-community/mathlib-AG
 
-src/combinatorics/ @leanprover-community/mathlib-CO
+src/combinatorics/      @leanprover-community/mathlib-CO
+
+src/probability/        @leanprover-community/mathlib-PR
+
+src/tactic/             @leanprover-community/mathlib-meta