chore: update codebuild mac runners and aws cdk version (#1070)

Signed-off-by: ayush-panta <ayushkp@amazon.com>

Author: ayush-panta

lib/utils.ts

@@ -67,7 +67,7 @@ export const getCodeBuildStacks = (accountId?: string): CodeBuildStackArgs[] =>
     amiSearchString: "", // Empty string since we're using buildImageString directly
     environmentType: codebuild.EnvironmentType.MAC_ARM,
     buildImageOS: BuildImageOS.MAC,
-    buildImageString: codebuild.MacBuildImage.BASE_14,
+    buildImageString: codebuild.MacBuildImage.BASE_15,
     fleetProps: {
       computeType: codebuild.FleetComputeType.MEDIUM,
       baseCapacity: getMacBaseCapacityForAccount(accountId)