Install arm64 Miniconda on M1 Macs

[jwodder]

Closes #129.

[yarikoptic]

Thanks! Have you tried it on any m1? (We have one for datalad)

[jwodder]

@yarikoptic Yes, and it seems to work.

[codecov-commenter]

Codecov Report

Base: 68.53% // Head: 67.88% // Decreases project coverage by -0.64% :warning:

Coverage data is based on head (88508f5) compared to base (21205bd). Patch coverage: 50.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #130 +/- ## ========================================== - Coverage 68.53% 67.88% -0.65% ========================================== Files 1 1 Lines 1392 1395 +3 Branches 336 337 +1 ========================================== - Hits 954 947 -7 - Misses 351 359 +8 - Partials 87 89 +2 ``` | [Impacted Files](https://codecov.io/gh/datalad/datalad-installer/pull/130?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=datalad) | Coverage Δ | | |---|---|---| | [src/datalad\_installer.py](https://codecov.io/gh/datalad/datalad-installer/pull/130/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=datalad#diff-c3JjL2RhdGFsYWRfaW5zdGFsbGVyLnB5) | `67.88% <50.00%> (-0.65%)` | :arrow_down: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=datalad). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=datalad)

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[yarikoptic]

Great, thanks!