Using assertSame to make assertion strict

[peter279k]

Change log

• Using the assertSame to make assertion equals strict.
• Fixing the following coding style via PHP_CodeSniffer:

FILE: ...hp/systemctl-php/src/Exception/UnitTypeNotSupportedException.php
----------------------------------------------------------------------
FOUND 1 ERROR AFFECTING 1 LINE
----------------------------------------------------------------------
 11 | ERROR | [x] Opening brace must not be followed by a blank
    |       |     line (PSR12.Classes.OpeningBraceSpace.Found)
----------------------------------------------------------------------
PHPCBF CAN FIX THE 1 MARKED SNIFF VIOLATIONS AUTOMATICALLY
----------------------------------------------------------------------

[icanhazstring]

Not required as phpunit 9 always does a strict comparison even with assertEquals. But ok