Fix G34 with Z_DUAL_STEPPER_DRIVERS compile (#16274)

Marlin/src/gcode/calibrate/G34_M422.cpp

@@ -85,8 +85,11 @@ static_assert(LTEST(0) && RTEST(0), "The 1st Z_STEPPER_ALIGN_XY X is unreachable
 static_assert(FTEST(0) && BTEST(0), "The 1st Z_STEPPER_ALIGN_XY Y is unreachable with the default probe Y offset.");
 static_assert(LTEST(1) && RTEST(1), "The 2nd Z_STEPPER_ALIGN_XY X is unreachable with the default probe X offset.");
 static_assert(FTEST(1) && BTEST(1), "The 2nd Z_STEPPER_ALIGN_XY Y is unreachable with the default probe Y offset.");
+
+#if ENABLED(Z_TRIPLE_STEPPER_DRIVERS)
   static_assert(LTEST(2) && RTEST(2), "The 3rd Z_STEPPER_ALIGN_XY X is unreachable with the default probe X offset.");
   static_assert(FTEST(2) && BTEST(2), "The 3rd Z_STEPPER_ALIGN_XY Y is unreachable with the default probe Y offset.");
+#endif
 
 //
 // G34 / M422 shared data