BUG: avoid copying in GEMV benchmarks

Author: ev-br

benchmarks/benchmarks.py

@@ -98,7 +98,7 @@ def time_axpy(self, n, variant):
 gemv_sizes = [100, 200, 400, 600, 800, 1000]
 
 def run_gemv(a, x, y, func):
-    res = func(1.0, a, x, y=y)
+    res = func(1.0, a, x, y=y, overwrite_y=True)
     return res