Set pullup on BTN_BACK pin (#15654)

Marlin/src/lcd/ultralcd.cpp

       SET_INPUT_PULLUP(BTN_ENC);
     #endif
 
+    #if BUTTON_EXISTS(BACK)
+      SET_INPUT_PULLUP(BTN_BACK);
+    #endif
+
     #if BUTTON_EXISTS(UP)
       SET_INPUT(BTN_UP);
     #endif

Marlin/src/libs/vector_3.cpp

 // Apply a rotation to the matrix
 void vector_3::apply_rotation(const matrix_3x3 &matrix) {
   const float _x = x, _y = y, _z = z;
-  x = _x * matrix.vectors[0][0] + _y * matrix.vectors[1][0] + _z * matrix.vectors[2][0];
-  y = _x * matrix.vectors[0][1] + _y * matrix.vectors[1][1] + _z * matrix.vectors[2][1];
-  z = _x * matrix.vectors[0][2] + _y * matrix.vectors[1][2] + _z * matrix.vectors[2][2];
+  *this = { matrix.vectors[0][0] * _x + matrix.vectors[1][0] * _y + matrix.vectors[2][0] * _z,
+            matrix.vectors[0][1] * _x + matrix.vectors[1][1] * _y + matrix.vectors[2][1] * _z,
+            matrix.vectors[0][2] * _x + matrix.vectors[1][2] * _y + matrix.vectors[2][2] * _z };
 }
 
 void vector_3::debug(PGM_P const title) {