DOC: Add release note about the fix for 32 bit float random variates.

Author: WarrenWeckesser

doc/release/upcoming_changes/20314.change.rst

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+Change in generation of random 32 bit floating point variates
+-------------------------------------------------------------
+There was bug in the generation of 32 bit floating point values from
+the uniform distribution that would result in the least significant
+bit of the random variate always being 0.  This has been fixed.
+
+This change affects the variates produced by the `random.Generator`
+methods ``random``, ``standard_normal``, ``standard_exponential``, and
+``standard_gamma``, but only when the dtype is specified as
+``numpy.float32``.