Use an appropriate tmpdir to generate test files

tests/test_OFStream.cpp

@@ -12,7 +12,7 @@ TEST_CASE("OFStream", "[language]")
 {
   SECTION("ofstream")
   {
-    const std::string basename = "ofstream_";
+    const std::string basename = std::filesystem::temp_directory_path().append("ofstream_");
     const std::string filename = basename + std::to_string(parallel::rank());
 
     // Ensures that the file is closed after this line