update undertow to newer version (#18409)

Author: wing328

modules/openapi-generator/src/main/resources/java-undertow-server/pom.mustache

@@ -29,7 +29,7 @@
         <version.logback>1.4.13</version.logback>
         <version.junit>4.13.2</version.junit>
         <version.mockito>2.1.0-beta.124</version.mockito>
-        <version.undertow>2.3.5.Final</version.undertow>
+        <version.undertow>2.3.12.Final</version.undertow>
         <version.jsonpath>2.2.0</version.jsonpath>
         <version.httpclient>4.5.13</version.httpclient>
         <version.httpasyncclient>4.1.2</version.httpasyncclient>

samples/server/petstore/java-undertow/pom.xml

@@ -29,7 +29,7 @@
         <version.logback>1.4.13</version.logback>
         <version.junit>4.13.2</version.junit>
         <version.mockito>2.1.0-beta.124</version.mockito>
-        <version.undertow>2.3.5.Final</version.undertow>
+        <version.undertow>2.3.12.Final</version.undertow>
         <version.jsonpath>2.2.0</version.jsonpath>
         <version.httpclient>4.5.13</version.httpclient>
         <version.httpasyncclient>4.1.2</version.httpasyncclient>