Fix caching pillar/grains which contain bytes

Use dump rather than dumps when storing to the cache, this makes it
symmetric with fetch and more importantly sets use_bin_type so that
loading will be able to distinguish between bytes and str correctly.

changelog/57918.fixed

@@ -0,0 +1,2 @@
+Use "use_bin_type" to differentiate between bytes and str when writing cache
+for pillar and grains.

salt/cache/localfs.py

@@ -60,7 +60,7 @@ def store(bank, key, data, cachedir):
     os.close(tmpfh)
     try:
         with salt.utils.files.fopen(tmpfname, "w+b") as fh_:
-            fh_.write(__context__["serial"].dumps(data))
+            __context__["serial"].dump(data, fh_)
         # On Windows, os.rename will fail if the destination file exists.
         salt.utils.atomicfile.atomic_rename(tmpfname, outfile)
     except IOError as exc:

tests/unit/cache/test_localfs.py

@@ -296,3 +296,27 @@ class LocalFSTest(TestCase, LoaderModuleMockMixin):
         # Now test the return of the contains function when key='key'
         with patch.dict(localfs.__opts__, {"cachedir": tmp_dir}):
             self.assertTrue(localfs.contains(bank="bank", key="key", cachedir=tmp_dir))
+
+    def test_mix_of_utf8_and_non_utf8_can_be_round_tripped(self):
+
+        tmp_dir = tempfile.mkdtemp(dir=RUNTIME_VARS.TMP)
+
+        data = {
+            # Any unicode, which ideally is invalid ascii.
+            "unicode": "áéí",
+            # Any bytes so long as they're not valid utf-8
+            "bytes": b"\xfe\x99\x00\xff",
+        }
+        bank = "bank"
+        key = "key"
+
+        self.addCleanup(shutil.rmtree, tmp_dir)
+        with patch.dict(localfs.__opts__, {"cachedir": tmp_dir}):
+            with patch.dict(
+                localfs.__context__, {"serial": salt.payload.Serial("msgpack")}
+            ):
+                localfs.store(bank, key, data, tmp_dir)
+
+                actual = localfs.fetch(bank, key, tmp_dir)
+
+        self.assertEqual(data, actual)