Add dcreager as red-knot CODEOWNER (#16807)

So that I can keep track of (and start help reviewing) red-knot PRs more
easily

Author: dcreager

.github/CODEOWNERS

@@ -18,6 +18,6 @@
 /python/py-fuzzer/ @AlexWaygood
 
 # red-knot
-/crates/red_knot* @carljm @MichaReiser @AlexWaygood @sharkdp
-/crates/ruff_db/ @carljm @MichaReiser @AlexWaygood @sharkdp
-/scripts/knot_benchmark/ @carljm @MichaReiser @AlexWaygood @sharkdp
+/crates/red_knot* @carljm @MichaReiser @AlexWaygood @sharkdp @dcreager
+/crates/ruff_db/ @carljm @MichaReiser @AlexWaygood @sharkdp @dcreager
+/scripts/knot_benchmark/ @carljm @MichaReiser @AlexWaygood @sharkdp @dcreager