Accept benign values that contain the word union

https://github.com/modxcms/revolution/issues/12121

A context key with the word "union" in it, e.g. "unionworkers", triggers many "SQL injection attempt detected" errors. As far as I know, a malicious SQL "union" keyword will always be following by a space. Perhaps checking for "union " (with a space) instead of "union" will solve some problems without sacrificing safety.