Unification of the search term for ProductSearch and AdvancedSearch on the search-results page

### Shopware Version

6.6.10.03, trunk

### Affected area / extension

Platform(Default)

### Actual behaviour

ProductSearch and the AdvancedSearch behave differently in the output of the search term on the search results page.
AdvancedSearch lower case the search term.
The normal Search not.

Just for your info:
We have adapted the acceptance tests so that the search term is written directly in lower case to avoid different results with and without AdvancedSearch.

This is the adjusted acceptance test:
https://github.com/shopware/shopware/pull/8421
which is already backported and merged into 6.7.0.0 and 6.6.x.
The tests where improved once again, but they are not yet in 6.6.x:
https://github.com/shopware/shopware/pull/8458

### Expected behaviour

ProductSearch and the AdvancedSearch should behave the same in the output of the search term on the search results page.

### How to reproduce

- search an uppercase searchterm like "Bo" with and without AdvancedSearch.
- click on the "Show all search results"-link
- compare the search string for both cases