Add compat to docstring for single-arg isapprox (JuliaLang#40659)

Co-authored-by: Simeon Schaub <[email protected]>

Author: 2 people

base/floatfuncs.jl

@@ -295,6 +295,9 @@ end
 Create a function that compares its argument to `x` using `≈`, i.e. a function equivalent to `y -> y ≈ x`.
 
 The keyword arguments supported here are the same as those in the 2-argument `isapprox`.
+
+!!! compat "Julia 1.5"
+    This method requires Julia 1.5 or later.
 """
 isapprox(y; kwargs...) = x -> isapprox(x, y; kwargs...)