gnu: synthv1: Use qt6 instead of qt5.

* gnu/packages/music.scm (synthv1)[inputs]: Remove qtbase-5 and qtsvg-5; add
qtbase and qtsvg.
[native-inputs]: Remove qttools-5; add qttools.

Signed-off-by: Christopher Baines <mail@cbaines.net>

gnu/packages/music.scm

@@ -2300,10 +2300,10 @@ (define-public synthv1
            alsa-lib
            new-session-manager
            liblo
-           qtbase-5
-           qtsvg-5))
+           qtbase
+           qtsvg))
     (native-inputs
-     (list pkg-config qttools-5))
+     (list pkg-config qttools))
     (home-page "https://synthv1.sourceforge.io")
     (synopsis "Polyphonic subtractive synthesizer")
     (description