Improve type stability of ConformanceTests.generate_element(::MPolyRing) (#2077)

Author: HechtiDerLachs

src/MPoly.jl

@@ -1468,7 +1468,7 @@ function ConformanceTests.generate_element(Rx::MPolyRing)
   len_bound = 8
   exp_bound = rand(1:5)
   len = rand(0:len_bound)
-  coeffs = [ConformanceTests.generate_element(R) for _ in 1:len]
+  coeffs = elem_type(R)[ConformanceTests.generate_element(R) for _ in 1:len]
   exps = [[rand(0:exp_bound) for _ in 1:num_gens] for _ in 1:len]
   return Rx(coeffs, exps)
 end