ci: enble LLVM download for windows-gnu hosts

[mati865]

Continuation of #132781

try-job: dist-i686-mingw
try-job: dist-x86_64-mingw

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[mati865]

Basically my plan is to do try build with dist so the artifacts get uploaded and then do another try but with test jobs.
If that fails, I think we should merge dist builders change only and then in later PR do the same for test jobs.

[Kobzol]

I would personally prefer to disable LLVM download on the dist runners, to exercise the LLVM build path regularly.

[mati865]

I think dist runners always build LLVM artifacts for download (at least that appears to be the case in #132781) despite using the same environment variable.
Even if that's not the case, changing it would be a bigger change that affects all platforms.

[Kobzol]

Yeah, just to clarify, what I meant was that we shouldn't change the behavior on dist runners - they should always build.