Fix `extraPythonPackages` support in the container test driver.
It triggered the following warning from `nixpkgs`:
```
python3Packages = throw "do not use python3Packages when building Python packages, specify each used package as a separate argument"; # do not remove
```
The following `callPackage` usage triggered the `throw`:
```
hostPackages.python3.pkgs.callPackage
```
The change to a regular `callPackage` i`nvocation fixes this issue.
Added a container test with a popular package to ensure compatibility in the future.
Closes: #5459
