Update SignUpOrSignin_DomainAllowlist.xml

Terminated regular expression to ensure only one email.  Also simplified the alternation for the domain and fixed the help text which did not include gmail even though the regex allowed it.

policies/sign-up-domain-allowlist/policy/SignUpOrSignin_DomainAllowlist.xml

@@ -12,7 +12,7 @@
     <ClaimsSchema>
       <ClaimType Id="email">
         <Restriction>
-          <Pattern RegularExpression="^[a-zA-Z0-9.!#$%&amp;'^_`{}~\-]+@(outlook[.]com|live[.]com|gmail[.]com)" HelpText="Please enter a email address from one of the following domains: outlook.com, live.com." />
+          <Pattern RegularExpression="^[a-zA-Z0-9.!#$%&amp;'^_`{}~\-]+@(outlook|live|gmail)\.com$" HelpText="Please enter an email address from one of the following domains: outlook.com, live.com, gmail.com." />
         </Restriction>
       </ClaimType>
     </ClaimsSchema>
@@ -44,4 +44,4 @@
       <SubjectNamingInfo ClaimType="sub" />
     </TechnicalProfile>
   </RelyingParty>
-</TrustFrameworkPolicy>
+</TrustFrameworkPolicy>