util/codegen, all: use latest year, not time.Now, in generated files

Updates #6865

Change-Id: I6b86c646968ebbd4553cf37df5e5612fbf5c5f7d
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