Update notebooks_to_exclude.txt

Added ./R.ipynb to excluded files

.github/workflows/notebooks_to_exclude.txt

@@ -31,6 +31,7 @@
 # and not designed to run end-to-end
 ./R-client.ipynb
 ./R-weather.ipynb
+./R.ipynb
 
 # Ignore any temporary notebook caches etc
 .ipynb_checkpoints