Fix: failing unit tests due to "stack-use-after-scope"

The return value of `get_rotation_mode_path` was stored in a
`blender::StringRef` which caused the memory of the string to
be freed to early.

Fix by returning a `blender::StringRef`

Interestingly this seems to be only an issue on ASAN builds.

Pull Request: https://projects.blender.org/blender/blender/pulls/116434

source/blender/animrig/ANIM_rna.hh

@@ -8,6 +8,7 @@
  * \brief Helper functions for animation to interact with the RNA system.
  */
 
+#include "BLI_string_ref.hh"
 #include "BLI_vector.hh"
 #include "DNA_action_types.h"
 #include "RNA_types.hh"
@@ -18,6 +19,6 @@ namespace blender::animrig {
 Vector<float> get_rna_values(PointerRNA *ptr, PropertyRNA *prop);
 
 /** Get the rna path for the given rotation mode. */
-std::string get_rotation_mode_path(eRotationModes rotation_mode);
+StringRef get_rotation_mode_path(eRotationModes rotation_mode);
 
 }  // namespace blender::animrig

source/blender/animrig/intern/anim_rna.cc

@@ -70,7 +70,7 @@ Vector<float> get_rna_values(PointerRNA *ptr, PropertyRNA *prop)
   return values;
 }
 
-std::string get_rotation_mode_path(const eRotationModes rotation_mode)
+StringRef get_rotation_mode_path(const eRotationModes rotation_mode)
 {
   switch (rotation_mode) {
     case ROT_MODE_QUAT: