Fix #2637

where testing.expect_value can't compare nils

tests/issues/test_issue_2637.odin

@@ -0,0 +1,13 @@
+// Tests issue #2637 https://github.com/odin-lang/Odin/issues/2637
+package test_issues
+
+import "core:testing"
+
+Foo :: Maybe(string)
+
+@(test)
+test_expect_value_succeeds_with_nil :: proc(t: ^testing.T) {
+  x: Foo
+  testing.expect(t, x == nil) // Succeeds
+  testing.expect_value(t, x, nil) // Fails, "expected nil, got nil"
+}