patch 8.0.0433: beeps when running tests

Problem:    Quite a few beeps when running tests.
Solution:   Set 'belloff' for these tests. (Christian Brabandt)
diff --git a/src/testdir/test73.in b/src/testdir/test73.in
index a0b9ae8..67fe455 100644
--- a/src/testdir/test73.in
+++ b/src/testdir/test73.in
@@ -2,6 +2,7 @@
 
 STARTTEST
 :so small.vim
+:set belloff=all
 :" Do all test in a separate window to avoid E211 when we recursively
 :" delete the Xfind directory during cleanup
 :"