Tests: fix RunCMake.CPack_DEB.EXTRA on Debian non-Linux OSes

The generated path with the packages uses $CPACK_TOPLEVEL_TAG, which
by default is $CPACK_SYSTEM_NAME, thus the OS name.

To make the expected stderr match also non-Linux OSes, accept any
non-slash characters in place of "Linux", so it works also on other
Debian OSes (e.g. Debian/Hurd).

Tests/RunCMake/CPack/tests/EXTRA/DEB-stderr.txt

@@ -1,6 +1,6 @@
 CPack Warning: Adding file to tar:
-#top level directory: .*/Tests/RunCMake/DEB.EXTRA/CPack/EXTRA-build/_CPack_Packages/Linux/DEB/extra-0.1.1-Linux/bas
+#top level directory: .*/Tests/RunCMake/DEB.EXTRA/CPack/EXTRA-build/_CPack_Packages/[^/]+/DEB/extra-0.1.1-[^/]+/bas
 #missing file: .*/Tests/RunCMake/DEB.EXTRA/CPack/EXTRA-build/conffiles
 CPack Warning: Adding file to tar:
-#top level directory: .*/Tests/RunCMake/DEB.EXTRA/CPack/EXTRA-build/_CPack_Packages/Linux/DEB/extra-0.1.1-Linux/foo
+#top level directory: .*/Tests/RunCMake/DEB.EXTRA/CPack/EXTRA-build/_CPack_Packages/[^/]+/DEB/extra-0.1.1-[^/]+/foo
 #missing file: .*/Tests/RunCMake/DEB.EXTRA/CPack/EXTRA-build/conffiles