doc: Suggest installing dev packages for debian/ubuntu qt5 build

Pretty much all library packages were renamed in the 64-bit time_t
migration to add `t64` (even on 64-bit platforms).

Instead of complicating the doc with conditional package names, suggest
installing the `-dev` packages which still have the same name, and
besides that, are the right way to go about it as they contain the
"user facing" C++ headers needed to build against Qt5.

For Fedora, devel packages are already suggested.

This affects Ubuntu 24.04 and Debian Testing.

doc/build-unix.md

@@ -81,7 +81,7 @@ To build without GUI pass `--without-gui`.
 
 To build with Qt 5 you need the following:
 
-    sudo apt-get install libqt5gui5 libqt5core5a libqt5dbus5 qttools5-dev qttools5-dev-tools
+    sudo apt-get install qtbase5-dev qttools5-dev qttools5-dev-tools
 
 Additionally, to support Wayland protocol for modern desktop environments: