Fixes namedtuple type name

[sobolevn]

The best practice is to match typename with variable name.
For example, mypy reports any other usages as errors: python/mypy#11206 (comment)

[nemacysts]

thanks for the PR!

for any code archaeologists in the future: the Python docs mention that the variable and typename should match:

To support pickling, the named tuple class should be assigned to a variable that matches typename.