mgr/dashboard: use system packages when running tox

Fixes: https://tracker.ceph.com/issues/70411
Signed-off-by: Nizamudeen A <[email protected]>

Author: nizamial09

src/pybind/mgr/dashboard/tox.ini

@@ -38,6 +38,7 @@ deps =
     -rrequirements-extra.txt
 passenv =
     PYTHONPATH
+sitepackages = true
 setenv =
     PYTHONPATH=$PYTHONPATH:../..
     CFLAGS = -DXMLSEC_NO_SIZE_T