math: add exp2 (#7321)

stdlib/math.pyi

@@ -41,6 +41,10 @@ if sys.version_info >= (3, 8):
 def erf(__x: _SupportsFloatOrIndex) -> float: ...
 def erfc(__x: _SupportsFloatOrIndex) -> float: ...
 def exp(__x: _SupportsFloatOrIndex) -> float: ...
+
+if sys.version_info >= (3, 11):
+    def exp2(__x: _SupportsFloatOrIndex) -> float: ...
+
 def expm1(__x: _SupportsFloatOrIndex) -> float: ...
 def fabs(__x: _SupportsFloatOrIndex) -> float: ...