Use enable_if to control what types can instantiate a template

Using a `static_assert(false, ...)` expression in the `else` block of a
`if constexpr` statement doesn't work. The `else` block is not protected by
the `constexpr`-ness of the `if`s, so it is always compiled. Consequently
it will always fail to compile.

Signed-off-by: Chris Burel <burelc@amazon.com>

Code/Tools/TestImpactFramework/Runtime/Code/Source/TestImpactClientSequenceReportSerializer.cpp

@@ -6,6 +6,7 @@
  *
  */
 
+#include <AzCore/std/typetraits/disjunction.h>
 #include <TestImpactFramework/TestImpactClientSequenceReportSerializer.h>
 #include <TestImpactFramework/TestImpactSequenceReportException.h>
 #include <TestImpactFramework/TestImpactUtils.h>
@@ -735,7 +736,11 @@ namespace TestImpact
         };
     }
 
-    template<typename PolicyStateType>
+    template<typename PolicyStateType, typename = AZStd::enable_if_t<AZStd::disjunction_v<
+        AZStd::is_same<PolicyStateType, SequencePolicyState>,
+        AZStd::is_same<PolicyStateType, SafeImpactAnalysisSequencePolicyState>,
+        AZStd::is_same<PolicyStateType, ImpactAnalysisSequencePolicyState>
+    >>>
     PolicyStateType DeserializePolicyStateType(const rapidjson::Value& serialPolicyStateType)
     {
         if constexpr (AZStd::is_same_v<PolicyStateType, SequencePolicyState>)
@@ -750,10 +755,6 @@ namespace TestImpact
         {
             return DeserializeImpactAnalysisSequencePolicyStateMembers(serialPolicyStateType);
         }
-        else
-        {
-            static_assert(false, "Template paramater must be a valid policy state type");
-        }
     }
 
     template<typename SequenceReportBaseType>