Fix Plain60 layout (#8854)

Fixes the LAYOUT_60_ansi_split_bs_rshift where the key next to right shift didn't work.

Co-authored-by: Maarten Dekkers <maartenn2001@gmail.com>

keyboards/maartenwut/plain60/plain60.h

@@ -46,7 +46,7 @@
     {k00, k01, k02, k03, k04, k05, k06, k07, k08, k09, k0a, k0b, k0c, k0d, k0e}, \
     {k10, k11, k12, k13, k14, k15, k16, k17, k18, k19, k1a, k1b, k1c, k1d, XXX}, \
     {k20, k21, k22, k23, k24, k25, k26, k27, k28, k29, k2a, k2b, XXX, k2d, XXX}, \
-    {k30, XXX, k32, k33, k34, k35, k36, k37, k38, k39, k3a, k3b, k3c, XXX, XXX}, \
+    {k30, XXX, k32, k33, k34, k35, k36, k37, k38, k39, k3a, k3b, k3c, k3d, XXX}, \
     {k40, k41, k42, XXX, XXX, XXX, k46, XXX, XXX, XXX, k4a, k4b, k4c, k4d, XXX}  \
 }