When inserting keys in the viewport by pressing `I`,
certain custom properties would not get keyed if their name
was identical to existing properties (for example `scale`).
That was because we use the name of the property to resolve
an rna path and check if the path resolved. This was of course
true in the described case and the square brackets would never be added.
The solution is to check for `RNA_property_is_runtime` which is false
for properties defined inside Blender.
Pull Request: https://projects.blender.org/blender/blender/pulls/135304
b834ca4fb1