Fix CI build by upgrading tonic-build to 0.8.4

[viirya]

Which issue does this PR close?

Closes #.

Rationale for this change

CI now failed by

error: failed to select a version for the requirement `tonic-build = "=0.8.3"`
candidate versions found which didn't match: 0.8.4, 0.8.2, 0.8.0, ...
location searched: crates.io index
required by package `arrow-flight v28.0.0 (/__w/arrow-rs/arrow-rs/arrow-flight)`

What changes are included in this PR?

Are there any user-facing changes?

[tustvold]

0.8.3 must have been yanked 😢

[ursabot]

Benchmark runs are scheduled for baseline = bdfe0fd and contender = 1a8e6ed. 1a8e6ed is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on ec2-t3-xlarge-us-east-2] ec2-t3-xlarge-us-east-2
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on test-mac-arm] test-mac-arm
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on ursa-i9-9960x] ursa-i9-9960x
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on ursa-thinkcentre-m75q] ursa-thinkcentre-m75q
Buildkite builds:
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python, R. Runs only benchmarks with cloud = True
test-mac-arm: Supported benchmark langs: C++, Python, R
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java