Update ci_build.yml

Change flutter version

Author: farzadi

.github/workflows/ci_build.yml

@@ -15,6 +15,7 @@ jobs:
           java-version: '12.x'
       - uses: subosito/[email protected]
         with:
+          flutter-version: '1.26.x' 
           channel: 'dev'
       - run: flutter pub get
       - run: flutter test