Use Servlet 6.0.

While we test against Jakarta EE 9 in one profile, we must, in fact, use Servlet 6.0 across the board.

Related: #1292.

Author: gregturn

pom.xml

@@ -276,7 +276,7 @@
                 <jakarta-mail-api.version>2.0.1</jakarta-mail-api.version>
                 <jakarta-mail-ee9-impl.version>2.0.1</jakarta-mail-ee9-impl.version>
                 <jakarta-mail-ee-10-impl.version>2.1.0</jakarta-mail-ee-10-impl.version>
-                <jakarta-servlet.version>5.0.0</jakarta-servlet.version>
+                <jakarta-servlet.version>6.0.0</jakarta-servlet.version>
                 <jakarta-soap.version>2.0.1</jakarta-soap.version>
                 <jakarta-xml-bind.version>3.0.1</jakarta-xml-bind.version>
             </properties>