clang-tidy: Enable modernize-raw-string-literal check

This check selectively replaces string literals containing
escaped characters with raw string literals.

Change-Id: I76fd4cde664f10390e36817044153d62380278bf
Signed-off-by: Pavithra Barithaya <pavithrabarithaya07@gmail.com>
diff --git a/test/systemd_parser.cpp b/test/systemd_parser.cpp
index cbe795c..7277f60 100644
--- a/test/systemd_parser.cpp
+++ b/test/systemd_parser.cpp
@@ -100,7 +100,7 @@
 TEST(TargetJsonParser, InvalidFileFormat)
 {
     std::FILE* tmpf = fopen("/tmp/invalid_json_file.json", "w");
-    std::fputs("{\"targets\":{\"missing closing quote}}", tmpf);
+    std::fputs(R"({"targets":{"missing closing quote}})", tmpf);
     fclose(tmpf);
 
     std::vector<std::string> filePaths;