Python: Fix problems with sinks in pathlib

This must mean that we did not have this flow with the old call-graph,
which means the new call-graph is doing a better job (yay).

python/ql/test/library-tests/frameworks/stdlib-py3/FileSystemAccess.py

@@ -13,7 +13,7 @@ with p.open() as f:  # $ getAPathArgument=p
 
 p.write_bytes(b"hello")  # $ getAPathArgument=p fileWriteData=b"hello"
 p.write_text("hello")  # $ getAPathArgument=p fileWriteData="hello"
-p.open("wt").write("hello")  # $ getAPathArgument=p fileWriteData="hello" SPURIOUS: getAPathArgument=self
+p.open("wt").write("hello")  # $ getAPathArgument=p fileWriteData="hello"
 
 name = windows.parent.name
 o = open