clang-tidy: Enable readability-redundant-string-cstr check

This check finds unnecessary calls to std::string::c_str().

Change-Id: I4bf2b9848ad6b6fa748f8e3bdd8d670cdeee90ff
Signed-off-by: Pavithra Barithaya <pavithrabarithaya07@gmail.com>
diff --git a/.clang-tidy b/.clang-tidy
index 1dec9a7..a5de905 100644
--- a/.clang-tidy
+++ b/.clang-tidy
@@ -247,6 +247,7 @@
 readability-redundant-member-init,
 readability-redundant-preprocessor,
 readability-redundant-smartptr-get,
+readability-redundant-string-cstr,
 readability-simplify-boolean-expr,
 readability-simplify-subscript-expr,
 readability-static-definition-in-anonymous-namespace,