Add missing CODEOWNER (#7016)

`shared_preferences_android` was accidentally missing a code owner.

CODEOWNERS

diff --git a/CODEOWNERS b/CODEOWNERS
index 2df1923..603e4a2 100644
--- a/CODEOWNERS
+++ b/CODEOWNERS
@@ -38,6 +38,7 @@
 packages/local_auth/local_auth_android/**                @camsim99
 packages/path_provider/path_provider_android/**          @camsim99
 packages/quick_actions/quick_actions_android/**          @camsim99
+packages/shared_preferences/shared_preferences_android/**  @reidbaker
 packages/url_launcher/url_launcher_android/**            @gmackall
 packages/video_player/video_player_android/**            @camsim99