dvc.stage.cache: fix typo, was using src filesystem to transfer

This was working for LocalFileSystem as they work for any directories/path.
It's hard to test this these days, as we don't have remote tests inside
dvc, so it was not caught.

Potentially fixes #7718.

dvc/stage/cache.py

@@ -216,7 +216,7 @@ def transfer(self, from_odb, to_odb):
         from dvc.fs.callbacks import Callback
 
         from_fs = from_odb.fs
-        to_fs = from_odb.fs
+        to_fs = to_odb.fs
         func = _log_exceptions(fs.generic.copy)
         runs = from_fs.path.join(from_odb.fs_path, "runs")
 

dvc/testing/test_run_cache.py

@@ -0,0 +1,19 @@
+import shutil
+
+from .tmp_dir import TmpDir
+
+
+def test_push_pull(tmp_dir, dvc, remote):
+    tmp_dir.gen("foo", "foo")
+    stage = dvc.stage.add(
+        deps=["foo"], outs=["bar"], name="copy-foo-bar", cmd="cp foo bar"
+    )
+    dvc.reproduce(stage.addressing)
+    assert dvc.push(run_cache=True) == 2
+
+    stage_cache_dir = TmpDir(dvc.stage_cache.cache_dir)
+    expected = list(stage_cache_dir.rglob("*"))
+    shutil.rmtree(stage_cache_dir)
+
+    dvc.pull(run_cache=True)
+    assert list(stage_cache_dir.rglob("*")) == expected