ADDED warning to RNG docs not to rely on the generated stream during …

…testing (#34670)

stdlib/Random/docs/src/index.md

@@ -26,6 +26,9 @@ unbounded integers, the interval must be specified (e.g. `rand(big.(1:6))`).
 Additionally, normal and exponential distributions are implemented for some `AbstractFloat` and
 `Complex` types, see [`randn`](@ref) and [`randexp`](@ref) for details.
 
+!!! warn
+    Because the precise way in which random numbers are generated is considered an implementation detail, bug fixes and speed improvements may change the stream of numbers that are generated after a version change. Relying on a specific seed or generated stream of numbers during unit testing is thus discouraged - consider testing properties of the methods in question instead.
+
 ## Random numbers module
 ```@docs
 Random.Random