Remove Redundant Pathspec from Doctest Collection

The `run_doctests.py` script was manually collecting the
`linearmoney.ext` module, but the extensions module is collected as part
of the root `linearmoney` module by pdoc, so this was redundant and was
causing a warning to be printed when running the `docs:test-in-source`
environment script.

This is fixed now.

documentation/run_doctests.py

@@ -58,7 +58,7 @@ def _run_module_doctests(module: pdoc.doc.Module):
 
 # Mostly copied from pdoc.pdoc() implementation:
 all_modules: list[pdoc.doc.Module] = []
-for module_name in pdoc.extract.walk_specs(["linearmoney", "linearmoney.ext"]):
+for module_name in pdoc.extract.walk_specs(["linearmoney"]):
     try:
         all_modules.append(pdoc.doc.Module.from_name(module_name))
     except RuntimeError: