VulpixUnitTests: Fix argument order for assertEquals

This small issue swaps labels in the error output and complicated fixing
failures.

Author: Blaisorblade

compiler/test/dotty/tools/vulpix/VulpixUnitTests.scala

@@ -91,7 +91,8 @@ class VulpixUnitTests extends ParallelTesting {
       fail()
     } catch {
       case ae: AssertionError =>
-        assertEquals(ae.getMessage, "Run test failed, but should not, reasons:\n  - test 'tests/vulpix-tests/unit/timeout.scala' timed out")
+        assertEquals("Run test failed, but should not, reasons:\n  - test 'tests/vulpix-tests/unit/timeout.scala' timed out",
+          ae.getMessage)
     }
   }
 }