profiles: element-desktop: allow /usr/share/element (#6424)

This path is apparently needed on openSUSE Tumbleweed[1]:

    $ LC_ALL=C firejail /usr/bin/element-desktop
    [...]
    Error launching app
    Unable to find Electron app at /usr/share/element/app

    Cannot find module '/usr/share/element/app'

    Parent is shutting down, bye...

Fixes #6421.

[1] https://software.opensuse.org/package/element-desktop

Reported-by: @leukimi

etc/profile-a-l/element-desktop.profile

@@ -14,6 +14,7 @@ noblacklist ${HOME}/.config/Element
 mkdir ${HOME}/.config/Element
 whitelist ${HOME}/.config/Element
 whitelist /opt/Element
+whitelist /usr/share/element
 
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