🎨(react) make eof stylesheets consistent

Some older tools misbehave if the last line of data
in a text file is not terminated with a newline.
It makes sure the last line was properly terminated.

.changeset/sweet-carrots-cheer.md

@@ -0,0 +1,5 @@
+---
+"@openfun/cunningham-react": patch
+---
+
+make eof stylesheet consistent with a newline