chore: clarifying panic message (gnolang#2051)

It should not happen but it did 😆 . This makes it easier to understand
why.
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pull request. -->

<details><summary>Contributors' checklist...</summary>

- [x] Added new tests, or not needed, or not feasible
- [x] Provided an example (e.g. screenshot) to aid review or the PR is
self-explanatory
- [x] Updated the official documentation or not needed
- [x] No breaking changes were made, or a `BREAKING CHANGE: xxx` message
was included in the description
- [x] Added references to related issues and PRs
- [x] Provided any useful hints for running manual tests
- [x] Added new benchmarks to [generated
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[here](https://github.com/gnolang/gno/blob/master/.benchmarks/README.md).
</details>

gnovm/pkg/gnolang/op_types.go

@@ -490,7 +490,7 @@ func (m *Machine) doOpStaticTypeOf() {
 		} else if _, ok := xt.(*TypeType); ok {
 			m.PushValue(asValue(gTypeType))
 		} else {
-			panic("should not happen")
+			panic("unexpected star expression")
 		}
 	case *RefExpr:
 		start := m.NumValues