[booster] Drop privileged SGID for non-privileged apps. Fixes JB#48847

Under Linux, setgid() is implemented like the POSIX version with the
_POSIX_SAVED_IDS feature. That means that after "setgid(nemo)" SGID
will be set to "privileged" instead of "nemo". So using "setresuid()"
instead.

Signed-off-by: Igor Zhbanov <i.zhbanov@omprussia.ru>

src/launcherlib/booster.cpp

@@ -521,7 +521,8 @@ void Booster::setEnvironmentBeforeLaunch()
         }
 
         if (getegid() != m_appData->groupId()) {
-            setgid(m_appData->groupId());
+            setresgid(m_appData->groupId(), m_appData->groupId(),
+                      m_appData->groupId());
         }
     }