Fix SSH_PUBKEYINFO, limit characters, add tests We fix a bad_bufptr() failure from a previous commit. We now limit the allowed characters to those that will definitely be safe in a shell. Some scripts/programs may use arbitrary environment variables without escaping correctly - that could be a problem in a restricted environment. The current allowed set is a-z A-Z 0-9 .,_-+@ This also adds a test for SSH_PUBKEYINFO, by default it only runs under github actions (or "act -j build").

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