[cmath] Rename positional-only param in log

Source: https://github.com/python/cpython/blob/790cdae5a0295586a55f00a57ed24a86b83928dc/Modules/cmathmodule.c#L864
Docs: https://docs.python.org/dev/library/cmath.html#cmath.log

Author: donbarbos

stdlib/cmath.pyi

@@ -23,7 +23,7 @@ def exp(z: _C, /) -> complex: ...
 def isclose(a: _C, b: _C, *, rel_tol: SupportsFloat = 1e-09, abs_tol: SupportsFloat = 0.0) -> bool: ...
 def isinf(z: _C, /) -> bool: ...
 def isnan(z: _C, /) -> bool: ...
-def log(x: _C, base: _C = ..., /) -> complex: ...
+def log(z: _C, base: _C = ..., /) -> complex: ...
 def log10(z: _C, /) -> complex: ...
 def phase(z: _C, /) -> float: ...
 def polar(z: _C, /) -> tuple[float, float]: ...