Make Flutter version input optional in setup-env action and rename step in workflow

.github/actions/setup-env.yaml

@@ -4,7 +4,7 @@ on:
   workflow_call:
     inputs:
       flutter_version:
-        required: true
+        required: false
         type: string
         default: "stable"
         description: "Flutter version to use. Default is 'stable'."

.github/workflows/flutter_test.yaml

@@ -13,7 +13,8 @@ jobs:
   test:
     runs-on: ubuntu-latest
     steps:
-      - uses: ./.github/actions/setup-env.yaml
+      - name: setup env
+        uses: ./.github/actions/setup-env.yaml
 
       # Debug: Echo current directory contents
       - name: List root directory contents