tidy: enable readability-redundant-string-init

See:
https://releases.llvm.org/14.0.0/tools/clang/tools/extra/docs/clang-tidy/checks/readability-redundant-string-init.html

src/.clang-tidy

@@ -5,6 +5,7 @@ misc-unused-using-decls,
 modernize-use-default-member-init,
 modernize-use-nullptr,
 readability-redundant-declaration,
+readability-redundant-string-init,
 '
 WarningsAsErrors: '
 bugprone-argument-comment,
@@ -12,4 +13,5 @@ misc-unused-using-decls,
 modernize-use-default-member-init,
 modernize-use-nullptr,
 readability-redundant-declaration,
+readability-redundant-string-init,
 '