Fix CI workflows for JDK 21 and headless javadoc build

.github/workflows/build.yml

@@ -11,7 +11,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     container:
-      image: eclipse-temurin:17-jdk
+      image: eclipse-temurin:21-jdk
 
     permissions:
       contents: read

.github/workflows/publish.yml

@@ -9,7 +9,7 @@ jobs:
   build-and-release:
     runs-on: ubuntu-latest
     container:
-      image: eclipse-temurin:17-jdk
+      image: eclipse-temurin:21-jdk
 
     permissions:
       contents: write

build.xml

@@ -195,8 +195,7 @@ POSSIBILITY OF SUCH DAMAGE.
     <target name="view.javadoc.local" description="view local package javadoc in web browser (NetBeans only)">
         <echo message="view local javadoc in ${dist.javadoc.dir} subdirectory"/>
         <!-- nbbrowse requires NetBeans IDE; commented out for headless/CI compatibility -->
-        <nbbrowse file="${dist.javadoc.dir}/index.html" />
-        <!-- nbbrowse file="${dist.javadoc.dir}/index.html" -->
+        <!-- <nbbrowse file="${dist.javadoc.dir}/index.html" /> -->
         <!-- TODO implementation-independent approach if possible, but note that other Ant approaches usually have to be customized for each OS. -->
     </target>
 

nbproject/project.properties

@@ -79,6 +79,7 @@ javac.test.classpath=\
     ${file.reference.apiguardian-api-1.1.0.jar}:\
     ${file.reference.junit-jupiter-api-5.7.0.jar}:\
     ${file.reference.junit-jupiter-engine-5.7.0.jar}:\
+    ${file.reference.opentest4j-1.2.0.jar}:\
     ${libs.junit_5.classpath}
 javac.test.modulepath=\
     ${javac.modulepath}