test pom.xml: Bump Surefire -Xmx

I'm seeing some GC overhead limit errors - more memory should solve that.

test/pom.xml

@@ -196,7 +196,7 @@ THE SOFTWARE.
         <artifactId>maven-surefire-plugin</artifactId>
         <!-- version specified in grandparent pom -->
         <configuration>
-          <argLine>${jacocoSurefireArgs} -Dfile.encoding=UTF-8 -Xmx256m -XX:MaxPermSize=128m</argLine>
+          <argLine>${jacocoSurefireArgs} -Dfile.encoding=UTF-8 -Xmx1g -XX:MaxPermSize=128m</argLine>
           <systemPropertyVariables>
               <!-- use AntClassLoader that supports predictable file handle release -->
               <hudson.ClassicPluginStrategy.useAntClassLoader>true</hudson.ClassicPluginStrategy.useAntClassLoader>