The previous workaround worked but prevented caching of every test
task as the value of system property pointing to the custom security
properties file varied from build to build.

This commit refines the workaround to copy the file into the build
directory of the test task's project and reference it using a URL
that's relative to the task's working directory. This ensures that
the value of the system property doesn't change from build to build.

Closes gh-26252