patch 8.2.4010: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more error messages to errors.h.
diff --git a/src/if_python.c b/src/if_python.c
index 63e9068..06d45d8 100644
--- a/src/if_python.c
+++ b/src/if_python.c
@@ -679,7 +679,7 @@
     if (python3_loaded())
     {
 	if (verbose)
-	    emsg(_("E836: This Vim cannot execute :python after using :py3"));
+	    emsg(_(e_this_vim_cannot_execute_python_after_using_py3));
 	return FAIL;
     }
 # endif