chore(ci): fix CodSpeed working directory (#2732)

Hey, I am a co-founder at @CodSpeedHQ, really glad to have you use it!

I checked out the repository after @hellovai contacted us, and found
there were an improvement that could be made to the setup!

## Changes
- bumped [`CodSpeedHQ/action`](https://github.com/CodSpeedHQ/action/) to
v4
- used the `working-directory` input instead of using `cd` inside the
`run` input

Thanks to those changes, you will normally benefit from [automated
profiling](https://codspeed.io/docs/instruments/walltime#automated-profiling)
on your benchmarks!

## Additional Notes

There is an issue with the benchmarks generated with
https://github.com/BoundaryML/baml/blob/514afc9dcbccd692dd7c59f53f69b45169984524/baml_language/crates/baml_tests/benches/compiler_benchmark.rs#L319,
their dashboard is not accessible because their URI is malformed (it
contains the whole path, eg:
`/actions-runner/_work/baml/baml/baml_language/target/release/build/baml_tests-74008be547e634ff/out/generated_benchmarks.rs::bench_incremental_add_attribute`).
We will take a look to at least try to make their dashboard work.

Author: adriencaccia

.github/workflows/ci.yaml

@@ -487,11 +487,12 @@ jobs:
         working-directory: baml_language
 
       - name: "Run benchmarks"
-        uses: CodSpeedHQ/action@v3
+        uses: CodSpeedHQ/action@v4
         with:
           mode: walltime
-          run: cd baml_language && cargo codspeed run
+          run: cargo codspeed run
           token: ${{ secrets.CODSPEED_TOKEN }}
+          working-directory: baml_language
 
   test-summary:
     name: "Test Summary"