need to fix issues in source tgz with the linked-dir

[pjfanning]

We had issues in the last pekko-http release with the linked dir used in testing. Seemed to only affect Windows users then but now, it's affecting Mac users.

x apache-pekko-http-1.0.1-RC1-incubating-src-20240126/http-tests/src/test/resources/dirWithLink/linked-dir: Truncated tar archive
tar: Error exit delayed from previous errors.

same dir that causes the issue in #275

[pjfanning]

I looked at sbt-source-dist and it might be possible to get it some symlinks - but I think we are better off rewriting the FileAndResourceDirectivesSpec so that it creates a temp dir that has all the files and symlinks set up by the test code before we run the main part of the test - i.e. remove the need for the symlink being checked into git and being reproduced in the tgz.