test: string number sample: change display instrument to violin (#949)

test/data/test_grace_note_fingerings_and_strings_Ysaye_excerpt.musicxml

@@ -42,10 +42,10 @@
     </defaults>
   <part-list>
     <score-part id="P1">
-      <part-name>Piano</part-name>
-      <part-abbreviation>Pno.</part-abbreviation>
+      <part-name>Violin</part-name>
+      <part-abbreviation>Vln.</part-abbreviation>
       <score-instrument id="P1-I1">
-        <instrument-name>Piano</instrument-name>
+        <instrument-name>Violin</instrument-name>
         </score-instrument>
       <midi-device id="P1-I1" port="1"></midi-device>
       <midi-instrument id="P1-I1">