[OTLP] Fix typo

Fix typo in CHANGELOG.

Co-authored-by: Copilot <[email protected]>

Author: martincostello

src/OpenTelemetry.Exporter.OpenTelemetryProtocol/CHANGELOG.md

@@ -7,7 +7,7 @@ Notes](../../RELEASENOTES.md).
 
 ## Unreleased
 
-* Fixed an issue where OTLP export of some metrics payloads to a some OTLP
+* Fixed an issue where OTLP export of some metrics payloads to some OTLP
   receivers were rejected with an HTTP 400 response due to gRPC protocol errors.
   ([#6567](https://github.com/open-telemetry/opentelemetry-dotnet/pull/6567))