cargo insta test cli: add --disable-nextest-doctest option

This adds an option to `cargo insta test` that prevents running doctests
with `cargo test` when Nextest is the test runner, even if the given
targets would ortherwise include doctests.

I usually use `cargo insta test` with `--test-runner nextest
--workspace` options. This always runs `cargo test --doc` after nextest
is done, and this takes a bit of time. This is an annoyance for me. I
think the project I work on might have a doctest or two, but they are
not very relevant, so I'm happy to rely on CI to catch any doctest
errors.

I only have a vague understanding of `cargo test` options, but I have
not found an existing set of test specifiers that's equivalent to
`--workspace --no-doctests-pretty-please`.

cargo-insta/src/cli.rs

@@ -168,6 +168,9 @@ struct TestCommand {
     /// Build for the target triple
     #[structopt(long)]
     target: Option<String>,
+    /// Do not run `cargo test --doc` after `cargo nextest`, even if test specifiers would otherwise include doctests.
+    #[structopt(long)]
+    disable_nextest_doctest: bool,
     /// Follow up with review.
     #[structopt(long)]
     review: bool,
@@ -818,6 +821,9 @@ fn prepare_test_runner<'snapshot_ref>(
         None
     };
     let mut prevents_doc_run = false;
+    if cmd.disable_nextest_doctest {
+        prevents_doc_run = true;
+    }
     if cmd.target_args.all || cmd.target_args.workspace {
         proc.arg("--all");
     }