Tests: Fix solver help output detection case insensitive (#5626) (#5627)

docs/CONTRIBUTORS

@@ -196,6 +196,7 @@ Srinivasan Venkataramanan
 Stefan Wallentowitz
 Stephen Henry
 Steven Hugg
+sumpster
 Szymon Gizler
 Sören Tempel
 Teng Huang

test_regress/driver.py

@@ -180,7 +180,7 @@ class Capabilities:
         if Capabilities._cached_have_solver is None:
             out = VtOs.run_capture('(z3 --help || cvc5 --help || cvc4 --help) 2>/dev/null',
                                    check=False)
-            Capabilities._cached_have_solver = bool('Usage' in out)
+            Capabilities._cached_have_solver = bool('usage' in out.casefold())
         return Capabilities._cached_have_solver
 
     @staticproperty