patch 8.2.3977: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more error messages to errors.h.
diff --git a/src/if_python3.c b/src/if_python3.c
index 938ab8d..3bf387a 100644
--- a/src/if_python3.c
+++ b/src/if_python3.c
@@ -1071,7 +1071,7 @@
 #ifdef DYNAMIC_PYTHON3
 	if (!python3_enabled(TRUE))
 	{
-	    emsg(_("E263: Sorry, this command is disabled, the Python library could not be loaded."));
+	    emsg(_(e_sorry_this_command_is_disabled_python_library_could_not_be_found));
 	    goto fail;
 	}
 #endif