Add regression test for issue 93274

Currently fails with:

    error: future cannot be sent between threads safely
      --> $DIR/src/test/ui/fmt/format-with-yield-point.rs:21:17
       |
    LL |     assert_send(with_await());
       |                 ^^^^^^^^^^^^ future returned by `with_await` is not `Send`
       |
       = help: the trait `Sync` is not implemented for `core::fmt::Opaque`
    note: future is not `Send` as this value is used across an await
      --> $DIR/src/test/ui/fmt/format-with-yield-point.rs:11:37
       |
    LL |     println!("{} {:?}", "", async {}.await);
       |     --------------------------------^^^^^^-
       |     |                               |
       |     |                               await occurs here, with `$crate::format_args_nl!($($arg)*)` maybe used later
       |     has type `ArgumentV1<'_>` which is not `Send`
       |     `$crate::format_args_nl!($($arg)*)` is later dropped here
    note: required by a bound in `assert_send`
      --> $DIR/src/test/ui/fmt/format-with-yield-point.rs:18:24
       |
    LL | fn assert_send(_: impl Send) {}
       |                        ^^^^ required by this bound in `assert_send`

    error: future cannot be sent between threads safely
      --> $DIR/src/test/ui/fmt/format-with-yield-point.rs:22:17
       |
    LL |     assert_send(with_macro_call());
       |                 ^^^^^^^^^^^^^^^^^ future returned by `with_macro_call` is not `Send`
       |
       = help: the trait `Sync` is not implemented for `core::fmt::Opaque`
    note: future is not `Send` as this value is used across an await
      --> $DIR/src/test/ui/fmt/format-with-yield-point.rs:6:17
       |
    LL |         async {}.await
       |                 ^^^^^^ await occurs here, with `$crate::format_args_nl!($($arg)*)` maybe used later
    ...
    LL |     println!("{} {:?}", "", m!());
       |     -----------------------------
       |     |                       |
       |     |                       in this macro invocation
       |     has type `ArgumentV1<'_>` which is not `Send`
       |     `$crate::format_args_nl!($($arg)*)` is later dropped here
    note: required by a bound in `assert_send`
      --> $DIR/src/test/ui/fmt/format-with-yield-point.rs:18:24
       |
    LL | fn assert_send(_: impl Send) {}
       |                        ^^^^ required by this bound in `assert_send`
       = note: this error originates in the macro `m` (in Nightly builds, run with -Z macro-backtrace for more info)

    error: aborting due to 2 previous errors

Author: dtolnay

src/test/ui/fmt/format-with-yield-point.rs

@@ -0,0 +1,23 @@
+// check-pass
+// edition:2021
+
+macro_rules! m {
+    () => {
+        async {}.await
+    };
+}
+
+async fn with_await() {
+    println!("{} {:?}", "", async {}.await);
+}
+
+async fn with_macro_call() {
+    println!("{} {:?}", "", m!());
+}
+
+fn assert_send(_: impl Send) {}
+
+fn main() {
+    assert_send(with_await());
+    assert_send(with_macro_call());
+}