package/fluidsynth: bump to version 2.1.3

package/fluidsynth: bump to version 2.1.3

Changes since v2.1.2:
https://github.com/FluidSynth/fluidsynth/releases/tag/v2.1.3
- fix a cross-compilation failure from Win32 to WinARM
- fix issues while fluid_player is seeking
- fix a NULL pointer dereference if synth.dynamic-sample-loading is enabled
- fix a NULL pointer dereference in delete_rvoice_mixer_threads()
- fix a NULL pointer dereference in the soundfont loader
- fix dsound driver playing garbage when terminating fluidsynth
- avoid memory leaks when using libinstpatch

./utils/test-pkg --package fluidsynth
6 builds, 1 skipped, 0 build failed, 0 legal-info failed

Signed-off-by: Julien Olivain <juju@cotds.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>