Update TestUtils.jl

Author: gaurav-arya

src/TestUtils.jl

@@ -43,7 +43,7 @@ a slightly modified dot test, in which case `real_plan=true` should be provided.
 function test_plan_adjoint end
 
 function __init__()
-    if isdefined(Base, :Experimental)
+    if isdefined(Base, :get_extension)
         # Better error message if users forget to load Test
         Base.Experimental.register_error_hint(MethodError) do io, exc, _, _
             if (exc.f === test_real_fft || exc.f === test_complex_fft) && Base.get_extension(AbstractFFTs, :AbstractFFTsTestExt) === nothing
@@ -53,4 +53,4 @@ function __init__()
     end
 end
 
-end
+end