chore: bump toolchain to nightly-2023-04-07

[xxchan]

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What's changed and what's your intention?

rust LLVM is updated to 16.0.2. Wanted to try this for #6205 (But it doesn't fix it 🤪

Documentation

• My PR DOES NOT contain user-facing changes.

Click here for Documentation

Types of user-facing changes

Please keep the types that apply to your changes, and remove the others.

• Installation and deployment
• Connector (sources & sinks)
• SQL commands, functions, and operators
• RisingWave cluster configuration changes
• Other (please specify in the release note below)

Release note

[xxchan]

Oh mama this is scary

[xxchan]

This is a regression in 2023-04-01, 2023-03-31 is ok

[xxchan]

Regression in 22a7a19f9333bc1fcba97ce444a3515cb5fb33e6
rust-lang/rust@22a7a19

searched nightlies: from nightly-2023-03-31 to nightly-2023-04-01
regressed nightly: nightly-2023-04-01
searched commit range: rust-lang/rust@ec2f40c...5e1d329
regressed commit: rust-lang/rust@22a7a19

bisected with cargo-bisect-rustc v0.6.6

Host triple: aarch64-apple-darwin
Reproduce with:

cargo bisect-rustc --script test.sh --start=2023-03-31 --end=2023-04-01 

[codecov]

Codecov Report

Merging #9051 (5365d04) into main (e294250) will increase coverage by 0.00%.
The diff coverage is 81.25%.

@@           Coverage Diff           @@
##             main    #9051   +/-   ##
=======================================
  Coverage   70.88%   70.88%           
=======================================
  Files        1197     1197           
  Lines      199012   199014    +2     
=======================================
+ Hits       141069   141072    +3     
+ Misses      57943    57942    -1     

Flag	Coverage Δ
rust	70.88% <81.25%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/cmd_all/src/lib.rs	100.00% <ø> (ø)
src/common/src/lib.rs	100.00% <ø> (ø)
src/connector/src/lib.rs	81.63% <ø> (ø)
src/expr/macro/src/lib.rs	92.85% <ø> (ø)
src/expr/src/lib.rs	100.00% <ø> (ø)
src/frontend/src/lib.rs	22.72% <ø> (ø)
src/frontend/src/scheduler/distributed/query.rs	69.57% <0.00%> (+0.32%)	⬆️
src/java_binding/src/lib.rs	0.29% <ø> (ø)
src/meta/src/lib.rs	0.90% <ø> (ø)
src/meta/src/rpc/service/hummock_service.rs	0.00% <0.00%> (ø)
... and 13 more

... and 34 files with indirect coverage changes

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