Newer versions of 7z fail to extract our dmg files because of the /Applications symlink

@ma1 found that the version of 7z included in Ubuntu 24.04 fails to extract our dmg files, in dmg2mar:

./rbm/rbm build release --step dmg2mar --target alpha --target signed --target torbrowser
Starting tor-browser-macos-14.5a1.dmg -> tor-browser-macos-14.5a1_ALL.mar
Error: Error extracting tor-browser-macos-14.5a1.dmg: ERROR: Dangerous link path was ignored : Tor Browser Alpha/Applications : /Applications

Error: Failed while running tor-browser-macos-14.5a1.dmg -> tor-browser-macos-14.5a1_ALL.mar
Error: Error running dmg2mar
make: *** [Makefile:238: torbrowser-dmg2mar-alpha] Error 1

We can workaround this by excluding the Applications symlink, which we don't include in the mar file.

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