Fix gpr_log compiler warning about string literals, which breaks the build

test/core/client_channel/resolvers/dns_resolver_cooldown_test.cc

@@ -285,7 +285,7 @@ static void start_test_under_work_serializer(void* arg) {
   gpr_log(GPR_DEBUG, "test: '%s' should be valid for '%s'", res_cb_arg->uri_str,
           factory->scheme());
   if (!uri.ok()) {
-    gpr_log(GPR_ERROR, uri.status().ToString().c_str());
+    gpr_log(GPR_ERROR, "%s", uri.status().ToString().c_str());
     GPR_ASSERT(uri.ok());
   }
   grpc_core::ResolverArgs args;

test/core/client_channel/resolvers/dns_resolver_test.cc

@@ -42,7 +42,7 @@ static void test_succeeds(grpc_core::ResolverFactory* factory,
   grpc_core::ExecCtx exec_ctx;
   absl::StatusOr<grpc_core::URI> uri = grpc_core::URI::Parse(string);
   if (!uri.ok()) {
-    gpr_log(GPR_ERROR, uri.status().ToString().c_str());
+    gpr_log(GPR_ERROR, "%s", uri.status().ToString().c_str());
     GPR_ASSERT(uri.ok());
   }
   grpc_core::ResolverArgs args;
@@ -61,7 +61,7 @@ static void test_fails(grpc_core::ResolverFactory* factory,
   grpc_core::ExecCtx exec_ctx;
   absl::StatusOr<grpc_core::URI> uri = grpc_core::URI::Parse(string);
   if (!uri.ok()) {
-    gpr_log(GPR_ERROR, uri.status().ToString().c_str());
+    gpr_log(GPR_ERROR, "%s", uri.status().ToString().c_str());
     GPR_ASSERT(uri.ok());
   }
   grpc_core::ResolverArgs args;