String patches are displayed incorrectly in Mixer with non-default soundfonts

1) Open Synthesizer, add some non-MuseScore soundfont (tested on FluidR3 GM2-2), remove all MuseScore_General soundfonts.
2) Create a score from Symphony orhestra template.

Result: all strings patches are listed in Mixer as a piano. If trying to add some notes and play the score strings are correctly played as strings.

The issue appeared after merging https://github.com/musescore/MuseScore/pull/5114 (for #290429: update ensemble strings instruments to select correct presets) since it specified bank numbers to instruments.xml and some templates (including Symphony orchestra). While selecting different banks seems to be necessary to distinguish between string instruments in MuseScore_General soundfont, it may work incorrectly with other soundfonts. It should probably be checked whether this leads to any more serious issues than this one and whether the solution can be corrected to work better with all soundfonts.