[partition] Don't translate placeholder ---

src/modules/partition/gui/VolumeGroupBaseDialog.ui

@@ -89,7 +89,7 @@
    <item row="4" column="2">
     <widget class="QLabel" name="totalSize">
      <property name="text">
-      <string>---</string>
+      <string notr="true">---</string>
      </property>
      <property name="alignment">
       <set>Qt::AlignCenter</set>
@@ -109,7 +109,7 @@
    <item row="5" column="2">
     <widget class="QLabel" name="usedSize">
      <property name="text">
-      <string>---</string>
+      <string notr="true">---</string>
      </property>
      <property name="alignment">
       <set>Qt::AlignCenter</set>
@@ -129,7 +129,7 @@
    <item row="6" column="2">
     <widget class="QLabel" name="totalSectors">
      <property name="text">
-      <string>---</string>
+      <string notr="true">---</string>
      </property>
      <property name="alignment">
       <set>Qt::AlignCenter</set>
@@ -149,7 +149,7 @@
    <item row="7" column="2">
     <widget class="QLabel" name="lvQuantity">
      <property name="text">
-      <string>---</string>
+      <string notr="true">---</string>
      </property>
      <property name="alignment">
       <set>Qt::AlignCenter</set>