Small followup fix to WL 5710:

  Test mysql_plugin failed if version string ended in -mN

mysql-test/t/mysql_plugin.test

@@ -288,11 +288,11 @@ let $MYSQL_PLUGIN_CMD= $MYSQL_PLUGIN -n --datadir=$MYSQL_DATADIR --basedir=$MYSQ
 --echo # Show the help.
 --echo #
 replace_result $MYSQL_PLUGIN mysql_plugin;
---replace_regex /Ver [0-9.]+ Distrib [0-9.]+/Ver V.V.VV Distrib XX.XX.XX/
+--replace_regex /Ver [0-9.]+ Distrib [0-9.]+/Ver V.V.VV Distrib XX.XX.XX/ /XX-m[0-9]+/XX/
 --exec $MYSQL_PLUGIN --help
 
 replace_result $MYSQL_PLUGIN mysql_plugin;
---replace_regex /Ver [0-9.]+ Distrib [0-9.]+/Ver V.V.VV Distrib XX.XX.XX/
+--replace_regex /Ver [0-9.]+ Distrib [0-9.]+/Ver V.V.VV Distrib XX.XX.XX/ /XX-m[0-9]+/XX/
 --exec $MYSQL_PLUGIN --version
 
 #