...
https://download.eclipse.org/ee4j/jakartaee-tck/8.0.1/nightly/servlettck-4.0_latest.zip
Or download the latest release build
https://download.eclipse.org/ee4j/jakartaee-tck/jakartaee10/promoted/epl/servlet-tck-6.0.0.zip
Extract to SERVLET_TCK_HOME
...