manifestcache: adding a second distinct entry

Let makes sure the cache can hold multiple value.

tests/test-manifest.t

@@ -124,3 +124,12 b" Check we don't duplicated entry (added f"
   cache contains 1 manifest entries, in order of most to least recent:
   id: 1e01206b1d2f72bd55f2a33fa8ccad74144825b7, size 133 bytes
   total cache data size 157 bytes, on-disk 157 bytes
+
+Adding a second entry
+
+  $ hg debugmanifestfulltextcache --add fce2a30dedad1eef4da95ca1dc0004157aa527cf
+  $ hg debugmanifestfulltextcache
+  cache contains 2 manifest entries, in order of most to least recent:
+  id: fce2a30dedad1eef4da95ca1dc0004157aa527cf, size 87 bytes
+  id: 1e01206b1d2f72bd55f2a33fa8ccad74144825b7, size 133 bytes
+  total cache data size 268 bytes, on-disk 268 bytes