executesql: use a different open sql file icon

The current one always looks to me as if the button is disabled.

src/MainWindow.ui

@@ -1438,7 +1438,7 @@
   <action name="actionSqlOpenFile">
    <property name="icon">
     <iconset resource="icons/icons.qrc">
-     <normaloff>:/icons/open_sql</normaloff>:/icons/open_sql</iconset>
+     <normaloff>:/icons/document_open</normaloff>:/icons/document_open</iconset>
    </property>
    <property name="text">
     <string>Open SQL file</string>

src/icons/icons.qrc

@@ -41,5 +41,6 @@
         <file alias="project_open">package_go.png</file>
         <file alias="field_key">page_key.png</file>
         <file alias="encryption">key.png</file>
+        <file alias="document_open">document-open.png</file>
     </qresource>
 </RCC>