Update the MAR signing key for 7.0
This should wait till the 7.0 series actually starts (and even a bit into then, since at least one MAR signature will be valid), but there is a new MAR key (#20589 (moved)), and the hard coded copies need to be kept in sync.
https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-45.6.0esr-6.5-1
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