ci: updated action scripts to use new path.

Author: kirstywilliams

.github/workflows/scripts/install-flutter.sh

@@ -10,4 +10,4 @@ then
 fi
 
 git clone https://github.com/flutter/flutter.git --depth 1 -b $BRANCH _flutter
-echo "::add-path::$GITHUB_WORKSPACE/_flutter/bin"
+echo "$GITHUB_WORKSPACE/_flutter/bin" >> $GITHUB_PATH

.github/workflows/scripts/install-tools.sh

@@ -1,6 +1,6 @@
 #!/bin/bash
 
 flutter pub global activate melos
-echo "::add-path::$HOME/.pub-cache/bin"
-echo "::add-path::$GITHUB_WORKSPACE/_flutter/.pub-cache/bin"
-echo "::add-path::$GITHUB_WORKSPACE/_flutter/bin/cache/dart-sdk/bin"
+echo "$HOME/.pub-cache/bin" >> $GITHUB_PATH
+echo "$GITHUB_WORKSPACE/_flutter/.pub-cache/bin" >> $GITHUB_PATH
+echo "$GITHUB_WORKSPACE/_flutter/bin/cache/dart-sdk/bin" >> $GITHUB_PATH