Install conda from miniforge rather than using old conda installation with a slow solver

[samanklesaria]

This PR is in response to #4083. The old version of conda used by pytorch-infra can't resolve the environment well enough to install ffmpeg, so we have to resort to the manual building step given by the ffmpeg github workflow. But @pearu thinks this problem could go away if we just used a more modern conda. This PR is a work in progress- it installs a fresh miniconda and attempts to activate it before building the rest of the docs.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/audio/4090

• 📄 Preview Python docs built from this PR

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❌ 6 New Failures

As of commit 6b7e190 with merge base 2e30055 ():

NEW FAILURES - The following jobs have failed:

• .github/workflows/bandit.yml (gh)
• .github/workflows/integration-test.yml (gh)
• .github/workflows/lint.yml (gh)
• .github/workflows/pr-labels.yml (gh)
• .github/workflows/unittest-windows-gpu.yml (gh)
• Build documentation / build / Build doc (gh)
  At least one of the pre-conditions you specified did not hold

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[pearu]

Replace

        echo "::group::Build FFmpeg"
        .github/scripts/ffmpeg/build_gpu.sh

with

conda install -q -y ffmpeg

It the doc build time will stay around 15 minutes (as it is now), building ffmpeg within torchaudio can be eliminated.

[samanklesaria]

Not working yet- it seems the system pip is still being used, not one associated with miniconda. In general, I find working with all the different kinds of conda spinoffs quite confusing; if I continue to encounter problems with the miniconda approach, I might just switch doing the build with pixi instead.

[pearu]

LGTM! Thanks, @samanklesaria!

Removing ffmpeg build can be finished in #4083 .

[pearu]

If waiting for green CI is blocking on #4083, I suggest merge this PR as the changes in this PR affects only docs build and it was successful (modulo a known test-infra issue).