Add missing Override annotation

[solth]

CodeQL reported:

Java enables you to annotate methods that are intended to override a method in a superclass. Compilers are required to generate an error if such an annotated method does not override a method in a superclass, which provides increased protection from potential defects. An annotated method also improves code readability.

This PR adds the missing annotation.

[stweil]

Is it required in SearchDatabaseService.java, too?

[stweil]

The build failure is unrelated to this PR (see issue #6138).

[solth]

Is it required in SearchDatabaseService.java, too?

Yes, probably. Thanks for pointing this out. Since there seem to be many more corresponding notes for missing Override annotations according to CodeQL however (at least 178 in the last report), I will not change them all in this PR but rather add a seperate PR to tackle the problem more comprehensively when I have time. This PR was just opened because this particular missing annotation was just reported recently.