update unit type

Author: alexander-alderman-webb

platform-includes/metrics/options/python.mdx

@@ -27,7 +27,7 @@ The metric dict has the following keys:
 - `name`: (`str`) The name of the metric.
 - `type`: (`str` - one of `counter`, `gauge`, `distribution`) The type of metric.
 - `value`: (`float`) The numeric value of the metric.
-- `unit`: (`int`) The unit of measurement for the metric value.
+- `unit`: (`str`) The unit of measurement for the metric value.
 - `attributes`: (`dict[str, str | bool | float | int]`) Additional attributes to be sent with the metric.
 - `timestamp`: (`float`) Timestamp in seconds (epoch time) indicating when the metric was recorded.
 - `trace_id`: (`Optional[str]`) The trace ID of the trace this metric belongs to.