Support building with Java 18

Also update the list of Java versions for the Github Actions build so
that it includes the current LTS versions and the latest version (i.e.
18).
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index f3f2c2b..16eaba8 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -27,7 +27,7 @@
   build:
     strategy:
       matrix:
-        java: [ 11, 15 ]
+        java: [ 11, 17, 18 ]
     name: "Java ${{ matrix.java }}"
     runs-on: ubuntu-18.04
     steps:
diff --git a/modules/jaxws-integration/pom.xml b/modules/jaxws-integration/pom.xml
index 3ac2019..1736417 100644
--- a/modules/jaxws-integration/pom.xml
+++ b/modules/jaxws-integration/pom.xml
@@ -1368,7 +1368,7 @@
                 <artifactId>maven-surefire-plugin</artifactId>
                 <inherited>true</inherited>
                 <configuration>
-                    <argLine>${argLine} -Xms256m -Xmx512m</argLine>
+                    <argLine>${argLine} -Xms256m -Xmx512m --add-opens java.desktop/java.awt=ALL-UNNAMED --add-opens java.xml/javax.xml.namespace=ALL-UNNAMED</argLine>
                     <!-- Enable the next 2 lines if you want to attach a debugger
                     <argLine>-Xdebug -Xnoagent -Djava.compiler=NONE -Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=5006</argLine>-->
                     <includes>