DOC: Clarify use of standard deviation in mtrand.pyx (numpy#27556)

* DOC: Clarifify use of standard deviation in mtrand.pyx

Previous texts mistakenly referred to the value as variance. Updated them to correctly reflect that standard deviation is being used. Removes confusion.

* DOC: Clarify use of standard deviation in _generator.pyx

Author: hairez

numpy/random/_generator.pyx

@@ -1258,7 +1258,7 @@ cdef class Generator:
         >>> rng = np.random.default_rng()
         >>> s = rng.normal(mu, sigma, 1000)
 
-        Verify the mean and the variance:
+        Verify the mean and the standard deviation:
 
         >>> abs(mu - np.mean(s))
         0.0  # may vary

numpy/random/mtrand.pyx

@@ -1547,7 +1547,7 @@ cdef class RandomState:
         >>> mu, sigma = 0, 0.1 # mean and standard deviation
         >>> s = np.random.normal(mu, sigma, 1000)
 
-        Verify the mean and the variance:
+        Verify the mean and the standard deviation:
 
         >>> abs(mu - np.mean(s))
         0.0  # may vary