Update MIRI pin

[tustvold]

Which issue does this PR close?

Closes #.

Rationale for this change

The git history does not really indicate why this was pinned, so lets unpin and see what breaks. This is currently blocking #1822

What changes are included in this PR?

Unpins miri version used in CI

Are there any user-facing changes?

No

[alamb]

If we set this to nightly, would that make it slightly easier to pin again?

[tustvold]

It's a one-line change either way so I don't think it really makes all that much difference

[alamb]

If MIRI passes this one looks good to me

[codecov-commenter]

Codecov Report

Merging #1828 (fb86bad) into master (c92943c) will increase coverage by 0.00%.
The diff coverage is n/a.

❗ Current head fb86bad differs from pull request most recent head e938c3d. Consider uploading reports for the commit e938c3d to get more accurate results

@@           Coverage Diff           @@
##           master    #1828   +/-   ##
=======================================
  Coverage   83.45%   83.45%           
=======================================
  Files         200      200           
  Lines       56719    56719           
=======================================
+ Hits        47334    47336    +2     
+ Misses       9385     9383    -2     

Impacted Files	Coverage Δ
parquet/src/encodings/encoding.rs	93.46% <0.00%> (-0.20%)	⬇️
arrow/src/datatypes/datatype.rs	65.79% <0.00%> (+0.37%)	⬆️
parquet_derive/src/parquet_field.rs	65.98% <0.00%> (+0.45%)	⬆️

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