Zstd v1.5.5 isn't detected correctly

[deepakm37]

Github runners on Ubuntu 20.04 are prepackaged with zstd v1.5.5 at the time of this writing. The command output of zstd --version has changed and it doesn't quite match the string that this action relies on (see here). As a result, zstd is assumed to be absent and slower gzip is used instead.

Please update the check to detect the presence of zstd.