Fix tests broken by Julia Base changes (#2844)

* Fix tests broken by Julia Base changes

* Update cat.jl

Author: bkamins

test/cat.jl

@@ -455,7 +455,7 @@ end
     df2 = @view df[:, 1:2]
     @test typeof(df1) != typeof(df2)
 
-    @test_throws ArgumentError reduce(vcat, ())
+    @test_throws Union{MethodError, ArgumentError} reduce(vcat, ())
     @test reduce(vcat, DataFrame[]) == DataFrame()
     @test reduce(vcat, SubDataFrame[]) == DataFrame()
     @test reduce(vcat, AbstractDataFrame[]) == DataFrame()

test/grouping.jl

@@ -1198,7 +1198,7 @@ Base.isless(::TestType, ::TestType) = false
         @test typeof(res.y) == typeof(expected.y)
         if m
             gd[1][:, :x1c] .= missing
-            @test_throws ArgumentError combine(gd, :x1c => f∘skipmissing => :y)
+            @test_throws Union{MethodError, ArgumentError} combine(gd, :x1c => f∘skipmissing => :y)
         end
     end
     @test combine(gd, :x1 => maximum => :y, :x2 => sum => :z) ≅