[ci] prepare: use Flutter 3.27.x instead of Flutter 3.19.x

Author: bartekpacia

.github/workflows/prepare.yaml

@@ -13,7 +13,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        flutter-version: ["3.19.x"]
+        flutter-version: ["3.27.x"]
 
     steps:
       - name: Clone repository