cephadm: pin flake8 to 5.0.4

to workaround zheller/flake8-quotes#110
flake8 v5.0.4 is the last known-to-work flake8 before flake8 v6.0.0.

Fixes: https://tracker.ceph.com/issues/58069
Signed-off-by: Kefu Chai <tchaikov@gmail.com>

src/cephadm/tox.ini

@@ -59,7 +59,7 @@ commands =
 basepython = python3
 allowlist_externals = bash
 deps =
-    flake8
+    flake8 == 5.0.4
     flake8-quotes
 commands =
     flake8 --config=tox.ini {posargs:cephadm.py}