fix clang-tidy cppcoreguidelines-explicit-virtual-functions warnings

Author: dbarker

exporters/otlp/src/otlp_grpc_client.cc

@@ -91,7 +91,7 @@ class OPENTELEMETRY_LOCAL_SYMBOL OtlpGrpcAsyncCallData : public OtlpGrpcAsyncCal
       result_callback;
 
   OtlpGrpcAsyncCallData() {}
-  virtual ~OtlpGrpcAsyncCallData() {}
+  ~OtlpGrpcAsyncCallData() override {}
 };
 }  // namespace
 #endif

exporters/otlp/test/otlp_grpc_log_record_exporter_test.cc

@@ -125,7 +125,7 @@ class OtlpMockTraceServiceStub : public proto::collector::trace::v1::MockTraceSe
   public:
     async_interface(OtlpMockTraceServiceStub *owner) : stub_(owner) {}
 
-    virtual ~async_interface() override = default;
+    ~async_interface() override = default;
 
     void Export(
         ::grpc::ClientContext *context,
@@ -188,7 +188,7 @@ class OtlpMockLogsServiceStub : public proto::collector::logs::v1::MockLogsServi
   public:
     async_interface(OtlpMockLogsServiceStub *owner) : stub_(owner) {}
 
-    virtual ~async_interface() override = default;
+    ~async_interface() override = default;
 
     void Export(
         ::grpc::ClientContext *context,