ci: Remove `ubuntu:bionic` from the test matrix?

[eitsupi]

Given that Ubuntu 18.04 is already EOL (devcontainers/images#90), isn't there a need to test all features on this base image?

features/.github/workflows/test-all.yaml

Lines 43 to 52 in 0668db5

	baseImage:
	[
	"ubuntu:bionic",
	"ubuntu:focal",
	"ubuntu:jammy",
	"debian:11",
	"debian:12",
	"mcr.microsoft.com/devcontainers/base:ubuntu",
	"mcr.microsoft.com/devcontainers/base:debian",
	]

[samruddhikhandale]

Good point, we should remove the deprecated/EOL images from the test matrix 👍
eitsupi Feel free to open a PR, if you are interested, thanks!