Update main.yml to use spaces instead of tabs

Author: mcbarton

.github/workflows/main.yml

@@ -257,7 +257,7 @@ jobs:
           micromamba create -n xeus-lite-host jupyterlite-core
           micromamba activate xeus-lite-host
           cd build/test
-	  # Fresh install browsers, and run Emscripten tests in them
+          # Fresh install browsers, and run Emscripten tests in them
           # This is to match the Emscripten build instructions, where
           # we run in a fresh browser, to stop any extra installed
           # stuff interferring with the running of the tests