go.toolchain.rev: bump for CVE-2023-39325

Updates tailscale/corp#15165

Change-Id: Ib001cfb44eb3e6d735dfece9bd3ae9eea13048c9
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
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Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f