about: enclose version number string between backticks

When the text is pasted on gitlab, it recognizes the version SHA and
places a hyperlink to the commit, which might facilitate unintended
references to be created.

By enclosing the string between backticks, gitlab does not recognize it.

Closes #1246

src/gui/gcal-application.c

@@ -150,7 +150,7 @@ build_system_information (void)
 {
   GString *str = g_string_new (NULL);
 
-  g_string_append_printf (str, "GNOME Calendar (%s)\n\n", VERSION);
+  g_string_append_printf (str, "GNOME Calendar (`%s`)\n\n", VERSION);
 
   if (g_file_test ("/.flatpak-info", G_FILE_TEST_EXISTS))
     g_string_append (str, "* Flatpak: yes\n");