Pin nightly version to bypass packed_simd build error

[viirya]

Which issue does this PR close?

Closes #1734.

Rationale for this change

There is building error on packed_simd with latest nightly. Before packed_simd publishes new release, our CI will be blocked by the errors. This is to unblock PRs.

What changes are included in this PR?

Are there any user-facing changes?

[viirya]

cc @sunchao

[viirya]

We can change back to latest nightly once packed_simd publishes new release with a fix. This is for unblocking PRs.

[codecov-commenter]

Codecov Report

Merging #1743 (ee51fcc) into master (a14a1d3) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1743   +/-   ##
=======================================
  Coverage   83.31%   83.31%           
=======================================
  Files         196      196           
  Lines       55961    55961           
=======================================
+ Hits        46624    46626    +2     
+ Misses       9337     9335    -2     

Impacted Files	Coverage Δ
arrow/src/array/transform/mod.rs	86.85% <0.00%> (+0.11%)	⬆️
arrow/src/datatypes/datatype.rs	65.79% <0.00%> (+0.37%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update a14a1d3...ee51fcc. Read the comment docs.

[sunchao]

LGTM, thanks @viirya !

[viirya]

Merging for unblocking other PRs. Thanks @sunchao