StringToLowerCase: Reduce string length limit

The string solver was consuming a very large amount of memory with the limit set to 10000;
this appears to be pure chance whether the solver picks a solution requiring universals to be
instantiated a large number of times. The other tests in this directory are already set to
limit string length to 1000, so I just do the same thing here.

Author: smowton

jbmc/regression/jbmc-strings/StringToLowerCase/test_dependency.desc

@@ -1,6 +1,6 @@
 CORE
 Test.class
---function Test.withDependency  --max-nondet-string-length 10000
+--function Test.withDependency  --max-nondet-string-length 1000
 ^EXIT=10$
 ^SIGNAL=0$
 assertion at file Test.java line 48 .*: SUCCESS