Replaced @aws/dexp by @aws/flare in codeowners, as part of the dexp renaming (#5162)

As part of the renaming of "DEXP" to "Flare", the team name on GitHub has changed, and so the codeowners file in this repository should be updated accordingly.

Author: Jurredr

.github/CODEOWNERS

@@ -5,9 +5,9 @@ codemodernizer/ @aws/elastic-gumby
 codetransform/ @aws/elastic-gumby
 codewhisperer/ @aws/codewhisperer-team
 
-mynah-ui/ @aws/dexp
-mynah-ui/package.json @aws/dexp @aws/elastic-gumby @aws/earlybird @aws/codewhisperer-team
-mynah-ui/package-lock.json @aws/dexp @aws/elastic-gumby @aws/earlybird @aws/codewhisperer-team
+mynah-ui/ @aws/flare
+mynah-ui/package.json @aws/flare @aws/elastic-gumby @aws/earlybird @aws/codewhisperer-team
+mynah-ui/package-lock.json @aws/flare @aws/elastic-gumby @aws/earlybird @aws/codewhisperer-team
 
 # nested within chat/, so needs to be after to take precedence
 amazonqFeatureDev/ @aws/earlybird