MINOR: [Go] Correct benchmark units from bits/s to bytes/s (apache#37479

)

### Rationale for this change

We're trying to clean up the set of units used in Conbench, and the Go benchmarks stick out as `b/s` (bits per second), but looking at 

https://github.com/apache/arrow/blob/602083be4f9630eda3edaf3ac18a660ccce91468/ci/scripts/go_bench_adapt.py#L86

it looks like they're actually in `B/s` (bytes per second).

### What changes are included in this PR?

Just changing the units submitted to Conbench

### Are these changes tested?

No, but the unit will be validated by the Conbench API

### Are there any user-facing changes?

No

Authored-by: Edward Visel <[email protected]>
Signed-off-by: Antoine Pitrou <[email protected]>

ci/scripts/go_bench_adapt.py

@@ -95,7 +95,7 @@ def _transform_results(self) -> List[BenchmarkResult]:
                     batch_id=batch_id,
                     stats={
                         "data": [data],
-                        "unit": "b/s",
+                        "unit": "B/s",
                         "times": [time],
                         "time_unit": "i/s",
                         "iterations": benchmark["Runs"],