Reduce test size for miri

This makes `cargo +nightly miri test` run in a more reasonable length
of time (<10 minutes on my machine). Before, testing with miri took
>30 minutes to complete. (I'm not sure how long it would have
ultimately taken; I killed the test at that point.)

tests/oper.rs

@@ -666,17 +666,21 @@ fn gemm_64_1_f() {
 fn gen_mat_mul_i32() {
     let alpha = -1;
     let beta = 2;
-    let sizes = vec![
-        (4, 4, 4),
-        (8, 8, 8),
-        (17, 15, 16),
-        (4, 17, 3),
-        (17, 3, 22),
-        (19, 18, 2),
-        (16, 17, 15),
-        (15, 16, 17),
-        (67, 63, 62),
-    ];
+    let sizes = if cfg!(miri) {
+        vec![(4, 4, 4), (4, 7, 3)]
+    } else {
+        vec![
+            (4, 4, 4),
+            (8, 8, 8),
+            (17, 15, 16),
+            (4, 17, 3),
+            (17, 3, 22),
+            (19, 18, 2),
+            (16, 17, 15),
+            (15, 16, 17),
+            (67, 63, 62),
+        ]
+    };
     for &(m, k, n) in &sizes {
         let a = range_i32(m, k);
         let b = range_i32(k, n);