[Julia][Temporary] Skip all instances of esmvaltool install Julia in CI testing (Circle and Github Actions)

[valeriupredoi]

Description

Workaround for #3746

Current information

libcurl >8.10 breaks Julia installations - see #3755

This PR is an alternative to pinning curl in our environment (the only purpose for that pin would be to fix Julia's issues for us, the pin may result in environment conflicts in the future).

Obsolete information

Currently Julia package installs are broken on at least two fronts, see comments in #3746 and my unsuccessful attempts at averting issues in #3747 - these are recent issues and they don't stem from a new version of Julia; if at all, it's actually rather hard to update it, due to env insolvency (latest Julia=1.10.4 can not be installed in our env). We can't have our tests constantly broken, so the peasant solution here is anything but elegant, but it is practical 🍺
I have also been pestering the NetCDF jll folk at JuliaGeo/NetCDF.jl#195

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[bouweandela]

Would it be a possibility to put an upper pin on the broken Julia dependency? Or is the issue not related to the release of a new version of a dependency?

[valeriupredoi]

@bouweandela good question: there are two issues:

• NetCDF segafults - and this is with Julia 1.9.3 and an old version of NetCDF 0.10 something, to be able to get a newer version of NetCDF and see if that also SegFaults we'd have to update the Julia version, which is kinda hard now (I'll try a pin a la >1.9.3 but I doubt that'll work)
• the second issue is this: Calls curl_multi_assign with null JuliaLang/Downloads.jl#260 - which seems to be affecting any sort of installation at the moment

Frankly, I am getting rather fed up with Julia at or end, so I might go radical and propose we consider it dead in the water until we get one dev that can work on its support (and know what they're doing, unlike me 😆 ) eg @dr-ko

[valeriupredoi]

Here's some more Julia-related findings:

• we actually have a modern Py3.12-compat in Add support for Python=3.12 #3501 with the latest Julia installed ie 1.10.4 - there I commented out RainFARM, as Julia package - see GA test - and nicely, NetCDF is picked up at the latest version 0.12, so RainFARM is holing on to the old NetCDF that now SegFaults (I'll open an issue there), though the second issue with curl and Julia still persists
• as we have it now, the env doesn't allow for a modern Julia 1.10.4, see my test in Try pin Julia #3752

So it's either this PR, or our tests keep redlining 😢

[valeriupredoi]

UPDATE: @bouweandela it seems that all our and others' troubles stem from one single place (not NetCDF.jll not other bits) - the new curl 8.10+ - pinning it to lower than that allows for all Julia gubbins be installed even with the old Julia 1.9.3 - see #3755 and Github Action - would you reckon we temporarily deactivate Jula installs (as from here) or pin curl in our environment?

[bouweandela]

Pinning curl seems better, let's not forget to unpin it asap.

[valeriupredoi]

Superseded by #3755