Run "rm -rf" in background to save time

.github/workflows/static.yml

@@ -43,8 +43,8 @@ jobs:
           sudo apt install -y -qq moreutils  # https://unix.stackexchange.com/questions/26728/prepending-a-timestamp-to-each-line-of-output-from-a-command
           echo -e "free -h:\n`free -h`" | ts
           echo
-          sudo rm -rf /usr/local/lib/android # release about 12 GB, cost 1min
-          sudo rm -rf /usr/share/dotnet # release about 1 GB, cost 2s
+          sudo rm -rf /usr/local/lib/android & # release about 12 GB, cost 1min
+          sudo rm -rf /usr/share/dotnet & # release about 1 GB, cost 2s
           echo -e "df -h:\n`df -h`" | ts
           echo
           echo "pwd: `pwd`" | ts