prober: speed up TestCRL ~450x by baking in some test keys

Fixes #16290
Updates tailscale/corp#28679

Change-Id: Ic90129b686779d0ed1cb40acf187cfcbdd39eb83
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