Math: test that it's possible to convert Vector<1, T> to T.

It's not (but should be).

src/Magnum/Math/Test/VectorTest.cpp

@@ -214,7 +214,11 @@ void VectorTest::constructOneComponent() {
 
     /* Implicit constructor must work */
     constexpr Vector1 vec = 1.0f;
-    CORRADE_COMPARE(vec, Vector1(1));
+    CORRADE_COMPARE(vec, Vector1{1.0f});
+
+    /* Conversion back must also work */
+    Float value = vec;
+    CORRADE_COMPARE(value, 1.0f);
 }
 
 void VectorTest::constructConversion() {