chore: fix release pipeline (#140)

## Description

Looks like we can not use a env variable for setting the "environment"
property because the value is evaluated by GitHub action before the
"STAGE" variable is set. See
actions/runner#1189

.github/workflows/release.yml

@@ -82,7 +82,7 @@ jobs:
     name: Deploy Storybook
     runs-on: ubuntu-latest
     needs: build
-    environment: ${{ env.STAGE }}
+    environment: ${{ github.ref_name == 'main' && 'prod' || 'dev' }}
     steps:
       - uses: actions/checkout@v4
 
@@ -109,7 +109,7 @@ jobs:
     name: Deploy documentation
     runs-on: ubuntu-latest
     needs: build
-    environment: ${{ env.STAGE }}
+    environment: ${{ github.ref_name == 'main' && 'prod' || 'dev' }}
     steps:
       - uses: actions/checkout@v4