add owner @open-telemetry/specs-semconv-maintainers to semantic-conventions owners (#287)

Co-authored-by: Armin Ruech <[email protected]>
Co-authored-by: Joao Grassi <[email protected]>

Author: 3 people

.github/CODEOWNERS

@@ -16,4 +16,4 @@
 *   @open-telemetry/specs-approvers
 
 # Owners for the semantic conventions generator tool
-/semantic-conventions/      @open-telemetry/specs-approvers @open-telemetry/specs-semconv-approvers
+/semantic-conventions/      @open-telemetry/specs-approvers @open-telemetry/specs-semconv-approvers @open-telemetry/specs-semconv-maintainers