[TEST] See if contrib tests break with a panic on configopaque fmt.Stringer impl

[mx-psi]

Description: A quick way to test implications of #9214

[mx-psi]

From https://pkg.go.dev/fmt#hdr-Format_errors:

If an Error or String method triggers a panic when called by a print routine, the fmt package reformats the error message from the panic, decorating it with an indication that it came through the fmt package. For example, if a String method calls panic("bad"), the resulting formatted message will look like

🙃 I am going to run the panic on a separate goroutine, since this way it can't be caught by recover

[mx-psi]

Alright, contrib tests are passing so it seems like there are no other usages of configopaque.String String method anywhere in contrib tests. That makes me a bit more certain that we have caught all usages