fix: follow symlink when searching for cases

[vpmapelli]

Hello,

At least from my undestanding, I believe that the How to use this repo implies that one could create a symbolic link for user's OpenFOAM cases in the same manner that it can be done for tests. I tried it in this manner, but I couldn't get the this expected behavior.

I have tracked down the cause to find command not following links. In that case, the simple addition of -L was enough for the correct inclusion of my cases to the test suite. I am creating this PR for you to evaluate whether it does make sense.

Btw, thank your for your time and this useful framework!

[FoamScience]

Thanks for using this thing!
There was a specific reason why cases are supposed to be copied into cases folder, and not symlinked into it.
BUT I don't remember what that reason was, If I can't remember - I'll accept this PR