snowflake: update to 2.6.0

snowflake: update to 2.6.0

Tor projects tries to migrate away from git.torproject.org [0,1]. We
need to adjust PKG_SOURCE and GO_PKG name. Further, we need to backport
patches to fix compiling on riscv64, so add:
- 0001-Bump-minimum-required-version-of-go.patch
- 0002-Update-dependencies.patch

Changelog:
https://gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake/-/commit/2fa8fd9188078eaa169f1edd16815deae4004c6c

[0] - https://gitlab.torproject.org/tpo/anti-censorship/team/-/issues/86
[1] - https://gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake/-/commit/82cc0f38f73c4ca4e12d22173562a092ebd4dea0

Signed-off-by: Nick Hainke <vincent@systemli.org>
(cherry picked from commit 0281f7594b31a5a947c26b895343daedc8a808e8)