Upgrade to tor 0.4.6.8

I have bumped the expiration date of the APT snapshot this MR switches to.

This MR upgrades tor, and only tor, as expected:

--- tails-amd64-stable@aeb20a24d2-20211103T0927Z.packages	2021-11-03 12:24:46.275355118 +0100
+++ tails-amd64-18310-tor-0.4.6+force-all-tests@8643f8a48c+stable@7457086d46-20211103T1045Z.packages	2021-11-03 12:24:27.462992742 +0100
@@ -1632,8 +1632,8 @@
 thunderbird-l10n-ru	1:78.14.0-1~deb10u1
 thunderbird-l10n-tr	1:78.14.0-1~deb10u1
 thunderbird-l10n-zh-cn	1:78.14.0-1~deb10u1
-tor	0.4.5.10-1~d10.buster+1
-tor-geoipdb	0.4.5.10-1~d10.buster+1
+tor	0.4.6.8-1~d10.buster+1
+tor-geoipdb	0.4.6.8-1~d10.buster+1
 torsocks	2.3.0-2
 totem	3.30.0-4
 totem-common	3.30.0-4

Closes #18310 (closed)