fix(mac-os): tag extraction for latest release in install.sh

[alessandromazza98]

Running the suggested install command in mac os gives this error:

❯ curl -sSfL https://raw.githubusercontent.com/flashbots/builder-playground/main/install.sh | bash
Fetching latest release...
grep: invalid option -- P
usage: grep [-abcdDEFGHhIiJLlMmnOopqRSsUVvwXxZz] [-A num] [-B num] [-C[num]]
        [-e pattern] [-f file] [--binary-files=value] [--color=when]
        [--context[=num]] [--directories=action] [--label] [--line-buffered]
        [--null] [pattern] [file ...]

This PR addresses this problem by removing the -P problematic flag with sed. This will keep compatibility with linux too.