fix: static_asserts fixed for the older compilers

src/core/include/mp-units/framework/quantity.h

@@ -171,7 +171,7 @@ public:
     requires(!DeltaReference<R2>)
   constexpr quantity(Value&&, R2)
   {
-    static_assert(false,
+    static_assert(DeltaReference<R2>,
                   "References using offset units (e.g., temperatures) must be explicitly qualified with `delta`");
   }
 

src/core/include/mp-units/framework/reference.h

@@ -224,7 +224,7 @@ template<typename Rep, Reference R>
 [[noreturn]] constexpr auto operator*(Rep&&, R)
 {
   static_assert(
-    false,
+    DeltaReference<R>,
     "References using offset units (e.g., temperatures) must be explicitly qualified with `delta` or `absolute`");
 }
 
@@ -233,7 +233,7 @@ template<typename Rep, Reference R>
 [[noreturn]] constexpr auto operator/(Rep&&, R)
 {
   static_assert(
-    false,
+    DeltaReference<R>,
     "References using offset units (e.g., temperatures) must be explicitly qualified with `delta` or `absolute`");
 }