cargo insta test: Cannot specify cargo profile when using `nextest` runner

`--profile` flag was introduced in #402 to specify cargo profile. However, when using ` --test-runner nextest`, this flag is interpreted as the nextest profile. This is confusing, but also as of `cargo-nextest 0.9.136` there is no way to specify the cargo profile in `nextest.toml`. IMO nextest profile should live under its own flag, e.g. `--nextest-profile`.