Suppress clang-tidy readability-convert-member-functions-to-static.

Some of the transcoder member functions could be made static because
they simply return a constant. However, I want to be consistent with
the documented transcoder API so they are not static. This change
suppresses warnings from clang-tidy when this is happening.

Author: paulhuggett

include/icubaby/icubaby.hpp

@@ -762,7 +762,8 @@ template <> class transcoder<char32_t, char8> {
   /// \returns True if the input represented well formed UTF-32.
   [[nodiscard]] constexpr bool well_formed () const noexcept { return well_formed_; }
   /// \returns True if a partial code-point has been passed to operator() and
-  /// false otherwise.
+  ///   false otherwise.
+  // NOLINTNEXTLINE(readability-convert-member-functions-to-static)
   [[nodiscard]] constexpr bool partial () const noexcept { return false; }
 
 private:
@@ -1005,7 +1006,8 @@ template <> class transcoder<char32_t, char16_t> {
   /// \returns True if the input represented valid UTF-32.
   [[nodiscard]] constexpr bool well_formed () const noexcept { return well_formed_; }
   /// \returns True if a partial code-point has been passed to operator() and
-  /// false otherwise.
+  ///   false otherwise.
+  // NOLINTNEXTLINE(readability-convert-member-functions-to-static)
   [[nodiscard]] constexpr bool partial () const noexcept { return false; }
 
 private: