tests: Move replacement policy tests to long/Nightly

These tests require the compilation of NULL with the MI_Example cache
coherence protocol. This is a large overhead for these tests. They are
therefore better off being run nightly rather than as a
pre-commit/kokoro/quick test.

Change-Id: I87b25afa313ecca65c738e3a8692a9bf72b06620
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/66615
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Matt Sinclair <mattdsinclair@gmail.com>

tests/gem5/replacement-policies/test_replacement_policies.py

@@ -51,7 +51,7 @@ def test_replacement_policy(config_name: str, config_path: str) -> None:
         valid_isas=(constants.null_tag,),
         protocol="MI_example",
         valid_hosts=constants.supported_hosts,
-        length=constants.quick_tag,
+        length=constants.long_tag,
     )