[processing][gdaltools] reword merge option (fix #8519)

Author: alexbruy

python/plugins/GdalTools/tools/widgetMerge.ui

@@ -84,7 +84,7 @@
    <item>
     <widget class="QCheckBox" name="separateCheck">
      <property name="text">
-      <string>Layer stack</string>
+      <string>Place each input file into a separate band</string>
      </property>
     </widget>
    </item>

python/plugins/processing/algs/gdal/merge.py

@@ -61,7 +61,7 @@ def defineCharacteristics(self):
         self.addParameter(ParameterBoolean(merge.PCT,
                                            self.tr('Grab pseudocolor table from first layer'), False))
         self.addParameter(ParameterBoolean(merge.SEPARATE,
-                                           self.tr('Layer stack'), False))
+                                           self.tr('Place each input file into a separate band'), False))
         self.addParameter(ParameterSelection(self.RTYPE,
                                              self.tr('Output raster type'), self.TYPE, 5))