[TASK] Fix support for bash v3 in runTests.sh

Bash hashtables are not supported in bash v4,
so we rather use a lookup function.

Resolves: #102502
Related: #102450
Releases: main, 12.4, 11.5
Change-Id: Id5c875b78ec655e15d225914626769720bbc3a81
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/81952


Tested-by: core-ci <typo3@b13.com>
Tested-by: Benjamin Franzke <ben@bnf.dev>
Reviewed-by: Benjamin Franzke <ben@bnf.dev>