[BUGFIX] PHP8.0 warning from ext:recycler tests

Initializing LanguageService in $GLOBALS['LANG'] with
Bootstrap::initalizeLanguageObject() needs a proper setup
$GLOBALS['BE_USER'].

The patch moves Bootstrap::initialzeLanguageObject() from
abstract testcase to the corresponding setUp() methods
user and admin recycler tests after the corresponding
backend user is set up.

Furthermore some assertions are fine tuned to prevent
array access warnings in tests.

Resolves: #95549
Releases: master
Change-Id: I3a9fed0a6f83e9481b169fb4a476ba2e2235e483
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/71519


Tested-by: Nikita Hovratov <nikita.h@live.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Jochen <rothjochen@gmail.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Nikita Hovratov <nikita.h@live.de>
Reviewed-by: Jochen <rothjochen@gmail.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>