ZD-6080620 Add rnngroup.ac.uk domain to email allowlist (#2781)

Author: DomBelcher

src/main/java/uk/gov/pay/adminusers/utils/email/EmailValidator.java

@@ -61,6 +61,7 @@ public class EmailValidator {
             "parliament.uk",
             "police.uk",
             "prrt.org",
+            "rnngroup.ac.uk",
             "scotent.co.uk",
             "serc.ac.uk",
             "slc.co.uk",

src/test/java/uk/gov/pay/adminusers/utils/email/EmailValidatorIsPublicSectorEmailTest.java

@@ -91,6 +91,7 @@ static Collection<Object[]> data() {
                 {"valid@parliament.uk", true},
                 {"valid@police.uk", true},
                 {"valid@prrt.org", true},
+                {"valid@rnngroup.ac.uk", true},
                 {"valid@scotent.co.uk", true},
                 {"valid@serc.ac.uk", true},
                 {"valid@slc.co.uk", true},
@@ -150,6 +151,7 @@ static Collection<Object[]> data() {
                 {"valid@subdomain.parliament.uk", true},
                 {"valid@subdomain.police.uk", true},
                 {"valid@subdomain.prrt.org", true},
+                {"valid@subdomain.rnngroup.ac.uk", true},
                 {"valid@subdomain.scotent.co.uk", true},
                 {"valid@subdomain.serc.ac.uk", true},
                 {"valid@subdomain.slc.co.uk", true},