Tag test as FUTURE instead of KNOWNBUG

The test times out with old versions ofz3
so we avoid running it while waiting for
bitwuzla in CI

Author: Remi Delmas

regression/contracts-dfcc/quantifiers-loops-fresh-bound-vars-smt/test.desc

@@ -1,4 +1,4 @@
-KNOWNBUG dfcc-only smt-backend broken-cprover-smt-backend
+FUTURE dfcc-only smt-backend broken-cprover-smt-backend
 main.c
 --dfcc main --apply-loop-contracts --enforce-contract foo --malloc-may-fail --malloc-fail-null _ --z3 --slice-formula --no-standard-checks
 ^EXIT=0$
@@ -8,7 +8,7 @@ main.c
 ^warning: ignoring
 --
 
-Marked as KNOWNBUG because:
+Marked as FUTURE because:
 - z3 >v4.12 and up can solve the problem with `--dfcc-simple-invalid-pointer-model`,
  but the CI uses older versions;
 - bitwuzla >v0.6 can solve the problem but we don't run bitwuzla in CI.