[BUGFIX] Do not try to download extensions in composer mode

Upgrade wizards that download extensions from TER must
no do so in composer mode as they would create an unusable
system.

But in case the extension is found, in the system, these wizards
still activate them.

Resolves: #82318
Releases: master, 8.7
Change-Id: I5ad1fdfeb81ad809497d8a88db32325639cd236b
Reviewed-on: https://review.typo3.org/56582


Reviewed-by: Mathias Brodala <mbrodala@pagemachine.de>
Tested-by: Mathias Brodala <mbrodala@pagemachine.de>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Joshua Westerheide <account@jdoubleu.de>
Tested-by: Joshua Westerheide <account@jdoubleu.de>
Reviewed-by: Daniel Goerz <ervaude@gmail.com>
Tested-by: Daniel Goerz <ervaude@gmail.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>