Ubuntu 20.04 support - pyqt5 update

[stephen3303]

I am trying to install gr-air-modes using pybombs (2.3.4) on Ubuntu 20.04 using gnuradio-defualt (GNU Radio Companion v3.8.2.0-78-gc4cc304c). It appears that 20.04 drops support for pyqt4. Recommend a PR to update to pyqt5.

name -a
Linux ubuntu 5.8.0-44-generic #50~20.04.1-Ubuntu SMP Wed Feb 10 21:07:30 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

/etc/os-release
NAME="Ubuntu"
VERSION="20.04.2 LTS (Focal Fossa)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 20.04.2 LTS"
VERSION_ID="20.04"

gnuradio@ubuntu:~/wifi$ pybombs inv
[INFO] Prefix Python version is: 3.8.5
[INFO] PyBOMBS Version 2.3.4
Showing package state:
uhd: installed
libvolk: installed
gnuradio: installed
gr-foo: installed
gr-ieee-80211: installed

gnuradio@ubuntu:~/wifi$ pybombs install gr-air-modes
[INFO] Prefix Python version is: 3.8.5
[INFO] PyBOMBS Version 2.3.4
[INFO] Phase 1: Creating install tree and installing binary packages:
[ERROR] Package has no install method: pyqt4-dev-tools