Change the git clone to sync to stable, and only to download the single branch

Author: jwren

tool/github.sh

@@ -9,10 +9,9 @@ set -e
 
 export JAVA_HOME=$JAVA_HOME_17_X64
 
-git clone --depth 1 https://github.com/flutter/flutter.git ../flutter
+git clone --depth 1 https://github.com/flutter/flutter.git -b stable --single-branch ../flutter
 export PATH="$PATH":`pwd`/../flutter/bin:`pwd`/../flutter/bin/cache/dart-sdk/bin
 flutter config --no-analytics
-flutter channel beta
 flutter doctor
 export FLUTTER_SDK=`pwd`/../flutter
 

tool/kokoro/setup.sh

@@ -20,10 +20,9 @@ setup() {
   java -version
 
   # If we move to branch-based builds we might not be able to use such a shallow clone.
-  git clone --depth 1 https://github.com/flutter/flutter.git ../flutter
+  git clone --depth 1 https://github.com/flutter/flutter.git -b stable --single-branch ../flutter
   export PATH="$PATH":`pwd`/../flutter/bin:`pwd`/../flutter/bin/cache/dart-sdk/bin
   flutter config --no-analytics
-  flutter channel beta
   flutter doctor
   export FLUTTER_SDK=`pwd`/../flutter