media-sound/easyeffects: (R)DEPEND on sci-libs/gsl

Needed alongside media-libs/speex (which by the way is technically
an *optional* dependency but given Easy Effects also have
a mandatory dependency on media-libs/speexdsp, adding IUSE=speex
would IMHO be confusing) since 7.0.0 but I forgot to paste that one
in.

With thanks to Xian Wang for having spotted this before me.

Closes: https://bugs.gentoo.org/880745
Signed-off-by: Marek Szuba <marecki@gentoo.org>

media-sound/easyeffects/easyeffects-7.0.0-r1.ebuild

@@ -38,6 +38,7 @@ COMMON="dev-cpp/nlohmann_json
 	media-libs/speexdsp
 	>=media-libs/zita-convolver-3.0.0
 	>=media-video/pipewire-0.3.41
+	sci-libs/gsl:=
 	sci-libs/fftw:3.0"
 # Only header files are used from libsamplerate
 DEPEND="${COMMON}