Update install.sh to support SETUP_FLUTTER_BRANCH

Author: socheatsok78

README.md

@@ -119,7 +119,7 @@ This action is designed to be used in GitHub Actions environment. If you want to
 # 
 # Example:
 
-SETUP_FLUTTER_BRANCH=main
+export SETUP_FLUTTER_BRANCH=main
 curl -fsSL https://raw.githubusercontent.com/flutter-actions/setup-flutter/${SETUP_FLUTTER_BRANCH}/install.sh | bash -s -- 3.0.2 stable
 ```
 

install.sh

@@ -1,4 +1,5 @@
 #!/bin/bash
+SETUP_FLUTTER_BRANCH=${SETUP_FLUTTER_BRANCH:-"main"}
 SETUP_FLUTTER_WORKDIR=${SETUP_FLUTTER_WORKDIR:-"$(pwd)/.setup-flutter"}
 
 # Runner environment variables
@@ -20,4 +21,4 @@ mkdir -p "$RUNNER_TOOL_CACHE" "$RUNNER_TEMP"
 touch "$GITHUB_ENV" "$GITHUB_PATH"
 
 # Run the action
-curl -fsSL "https://raw.githubusercontent.com/flutter-actions/setup-flutter/main/action.sh" | bash -s -- "$@"
+curl -fsSL "https://raw.githubusercontent.com/flutter-actions/setup-flutter/${SETUP_FLUTTER_BRANCH}/action.sh" | bash -s -- "$@"