Use Python 3.10 beta 4 instead of beta 1 in CI (#5839)

Quote all Python versions to make sure they are interpreted as strings,
not floats.

stdlib/statistics.pyi

@@ -82,6 +82,6 @@ if sys.version_info >= (3, 10):
     def correlation(__x: Sequence[_Number], __y: Sequence[_Number]) -> float: ...
     def covariance(__x: Sequence[_Number], __y: Sequence[_Number]) -> float: ...
     class LinearRegression(NamedTuple):
-        intercept: float
         slope: float
+        intercept: float
     def linear_regression(__regressor: Sequence[_Number], __dependent_variable: Sequence[_Number]) -> LinearRegression: ...