Fix provider format regex

Author: KostasTsiounis

closed/src/java.base/share/classes/openj9/internal/security/RestrictedSecurity.java

@@ -1807,7 +1807,7 @@ private static void checkProviderFormat(String providerInfo, boolean update) {
                 + "(\\["                                // constraints [optional]
                     + "\\s*"
                     + "([+-])?"                         // action [optional]
-                    + "[A-Za-z0-9{}.=*|:,/_\\s-]+"      // constraint definition
+                    + "[A-Za-z0-9{}.=*|:,/\\\\_\\s-]+"      // constraint definition
                 + "\\])?"
                 + "\\s*"
                 + "$");