Cleanup: spelling in comments

Also include "release/" in the `check_spelling_py` target.

GNUmakefile

@@ -502,6 +502,7 @@ check_spelling_py: .FORCE
 	    "$(BLENDER_DIR)/tools/check_source/check_spelling.py" \
 	    --cache-file=$(CHECK_SPELLING_CACHE) \
 	    --match=".*\.(py)$$" \
+	    "$(BLENDER_DIR)/release" \
 	    "$(BLENDER_DIR)/scripts" \
 	    "$(BLENDER_DIR)/source" \
 	    "$(BLENDER_DIR)/tools"