Vk: properly skip an assertion test case on a build w/o asserts.

The "no assert" build on the CIs doesn't test Vulkan, so this didn't get
caught.

src/Magnum/Vk/Test/PipelineVkTest.cpp

@@ -153,6 +153,10 @@ void PipelineVkTest::constructRasterization() {
 }
 
 void PipelineVkTest::constructRasterizationViewportNotSet() {
+    #ifdef CORRADE_NO_ASSERT
+    CORRADE_SKIP("CORRADE_NO_ASSERT defined, can't test assertions");
+    #endif
+
     MeshLayout meshLayout{MeshPrimitive::Triangles};
 
     PipelineLayout pipelineLayout{device(), PipelineLayoutCreateInfo{}};