prevent double ^ when using embroider test-setup

[mansona]

After the last release @embroider/test-setup was outputting a double ^ for the embroider versions like this:

"@embroider/core": "^^3.0.0",
"@embroider/webpack": "^^3.0.0",
"@embroider/compat": "^^3.0.0"

I don't know if any other packagers are more lenient about this but pnpm is very unhappy, so we should remove the extra carat 👍

[backspace]

Thanks for fixing this, I was puzzled seeing ERR_PNPM_SPEC_NOT_SUPPORTED_BY_ANY_RESOLVER in CI because of the ^^.