radicale: Allow older 2.x release to upgrade to 3.x

Tests performed:

- Upgrade from old 2.x versions to 3.x has not been tested.

- Fresh installation of radicale 3 works (via FreedomBox). Web interface works.
Able to create a calendar.

- Upgrading from radicale 2 to radicale 3 works (via unattended-upgrades). There
were no configuration file prompts in FreedomBox (where only
/etc/radicale/config is modified).

- After upgrade, all functional test cases for radicale in FreedomBox
passed (including backup and restore of data).

- After upgrade, I have tested that permissions system as configured in
FreedomBox owner_only = allow file permissions, owner_write and authorized are
same as defined in radicale.

- These permissions have worked as expected as tested with Thunderbird.

- Radicale says that file based permissions format has changed, however,
FreedomBox relies on only the right files provided by default.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Tested-by: Sunil Mohan Adapa <sunil@medhas.org>

plinth/modules/radicale/__init__.py

@@ -107,9 +107,9 @@ def force_upgrade(helper, packages):
     if 'radicale' not in packages:
         return False
 
-    # Allow upgrade from 2.* to newer 2.*
+    # Allow upgrade from 2.* to newer 2.* and 3.*
     package = packages['radicale']
-    if Version(package['new_version']) > Version('3~'):
+    if Version(package['new_version']) > Version('4~'):
         return False
 
     rights = get_rights_value()