Maintenance: Bump versions across the board

[thorstenhater]

We will remove support for the following in ~0.7~ 0.8

• [x] python 3.6. EOL reached
• [ ] CUDA 10
• [ ] GCC 8
• [ ] Clang 8
• [ ] Apple 9

and bump these by one each.

[brenthuisman]

For Python we don't and shouldn't care about upstream EOL.

We have a set of criteria laid out here. At this moment, Ubuntu LTS-1 is 18.04 which comes with Python 3.6. v0.7 might roughly coincide with a new Ubuntu LTS, so I just might allow it :)

In any case, I'd like see, for each tool deprecation, whether or not it has consequences for the platforms we want to support.

[thorstenhater]

Re: True, but that was the motivator.

Rest: all HPC systems we have access to are on CUDA11 now and we never liked GCC8 anyhow.

[bcumming]

I endorse all the above deprecations.

[brenthuisman]

Let's first close https://github.com/arbor-sim/arbor/issues/1731.

[brenthuisman]

For the moment: having Python 3.6 is helpful at Ebrains.

[thorstenhater]

This should absolutely be part of 0.8, these compilers are starting to reek.

[brenthuisman]

At the past Dev Meet, no particular attachment to these compilers were raised (@llandsmeer will check if CUDA 10 is a potential problem, but he didn't think so). So, shall I +1 each of these?

[thorstenhater]

YES! It's been orverdue to do that.

[llandsmeer]

We're on CUDA 11.5 on the development machine, so should be fine