[fixPkgName] Improvements to CI ()

Merging branch 'fixPkgName'  into 'main'.

* Corrected and unified the name of the installer on all platforms.  
  The installer name is `<Project-Name>-<Project-Version>-python<Python-Version>-<architecture>`; e.g.,
  `BornAgain-20.0-python3.11-linux_x64.sh` on Debian or `BornAgain-20.0-python3.9-mac_arm.dmg` on MacOS-M1.
* Corrected the path of Qt on Debian CI-machine since the required Qt plugins were not found due to an incorrect Qt path.
*  MacOS:  
   * Added linker flags to remove unneeded symbols/objects and dynamically-linked libraries.
   * Increased the minimum OSX version to 11.
   * Renamed the OS label to `mac` (instead of `macosx`).
* Corrected the installation directory for man pages on Linux, so that no root access is required.
* Slightly improved CI scripts.

See merge request !1558