Improve TestSwiftMutablePersistentVar (NFC)

Author: adrian-prantl

lldb/test/API/lang/swift/expression/mutable_persistent_var/TestSwiftMutablePersistentVar.py

@@ -4,11 +4,14 @@
 import lldbsuite.test.lldbutil as lldbutil
 
 
-class TestCase(TestBase):
+class TestSwiftMutablePersistentVar(TestBase):
+    NO_DEBUG_INFO_TESTCASE = True
     @swiftTest
     def test(self):
         """Test that persistent variables are mutable."""
         self.build()
         lldbutil.run_to_name_breakpoint(self, "main")
         self.expect("expr var $count = 30")
         self.expect("expr $count = 41")
+        self.expect("expr $count += 1")
+        self.expect("expr $count", substrs=["42"])