Rollup merge of #130219 - ogoffart:missing-docs-test, r=Urgau

Fix false positive with `missing_docs` and `#[test]`

Since #130025, the compiler don't ignore missing_docs when compiling the tests. But there is now a false positive warning for every `#[test]`

For example, this code
```rust
//! Crate docs

fn just_a_test() {}
```

Would emit this warning when running `cargo test`

```
warning: missing documentation for a constant
 --> src/lib.rs:5:1
  |
4 | #[test]
  | ------- in this procedural macro expansion
5 | fn just_a_test() {}
  | ^^^^^^^^^^^^^^^^^^^
```

tests/pretty/tests-are-sorted.pp

@@ -12,6 +12,7 @@ extern crate std;
 extern crate test;
 #[cfg(test)]
 #[rustc_test_marker = "m_test"]
+#[doc(hidden)]
 pub const m_test: test::TestDescAndFn =
     test::TestDescAndFn {
         desc: test::TestDesc {
@@ -36,6 +37,7 @@ fn m_test() {}
 extern crate test;
 #[cfg(test)]
 #[rustc_test_marker = "z_test"]
+#[doc(hidden)]
 pub const z_test: test::TestDescAndFn =
     test::TestDescAndFn {
         desc: test::TestDesc {
@@ -61,6 +63,7 @@ fn z_test() {}
 extern crate test;
 #[cfg(test)]
 #[rustc_test_marker = "a_test"]
+#[doc(hidden)]
 pub const a_test: test::TestDescAndFn =
     test::TestDescAndFn {
         desc: test::TestDesc {
@@ -83,7 +86,7 @@ pub const a_test: test::TestDescAndFn =
 fn a_test() {}
 #[rustc_main]
 #[coverage(off)]
-#[allow(missing_docs)]
+#[doc(hidden)]
 pub fn main() -> () {
     extern crate test;
     test::test_main_static(&[&a_test, &m_test, &z_test])

tests/ui/lint/lint-missing-doc-test.rs

@@ -2,4 +2,9 @@
 //! on the generated test harness.
 
 //@ check-pass
-//@ compile-flags: --test -Dmissing_docs
+//@ compile-flags: --test
+
+#![forbid(missing_docs)]
+
+#[test]
+fn test() {}