test: add regress test for reported non-monomorphizable example
test: add regress test for reported non-monomorphizable example

Fixes #48711.

Change-Id: I2ed1ef5267343d4b9f91da0618905098d178db90
Reviewed-on: https://go-review.googlesource.com/c/go/+/362394
Trust: Matthew Dempsky <e56ac2c500064424afac424d4b5e53bd0570a731@google.com>
Run-TryBot: Matthew Dempsky <e56ac2c500064424afac424d4b5e53bd0570a731@google.com>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>

golang/go,cloudflare/go,cloudflare/go,nawawi/go,golang/go,CAFxX/go,nawawi/go,golang/go,CAFxX/go,cloudflare/go,cloudflare/go,nawawi/go,cloudflare/go,CAFxX/go,golang/go,CAFxX/go,golang/go,nawawi/go,golang/go,nawawi/go,CAFxX/go,CAFxX/go,cloudflare/go,nawawi/go,cloudflare/go,golang/go,CAFxX/go,cloudflare/go,CAFxX/go,golang/go,nawawi/go,nawawi/go