Fix GEMM test templates to use variable n instead of fixed NR and regenerate tests

Also bump shard_count on qu8_igemm_minmax_rndnu_test as it is hitting timeouts.

PiperOrigin-RevId: 421606761
diff --git a/BUILD.bazel b/BUILD.bazel
index b88321d..3c592d9 100644
--- a/BUILD.bazel
+++ b/BUILD.bazel
@@ -11858,6 +11858,7 @@
         "test/qu8-igemm-minmax-rndnu.cc",
         "test/qu8-igemm-minmax-rndnu-2.cc",
     ] + WEIGHTS_PACK_HDRS + MICROKERNEL_TEST_HDRS,
+    shard_count = 2,
     deps = MICROKERNEL_TEST_DEPS + [
         ":gemm_microkernel_tester",
     ],