Rename doctest attribute standalone-crate into standalone_crate for coherency

tests/rustdoc-ui/doctest/standalone-warning-2024.rs

@@ -11,6 +11,6 @@
 //! bla
 //! ```
 //!
-//! ```standalone_crate
+//! ```standalone-crate
 //! bla
 //! ```

tests/rustdoc-ui/doctest/standalone-warning-2024.stderr

@@ -5,12 +5,12 @@ error: unknown attribute `standalone`
 11 | | //! bla
 12 | | //! ```
 13 | | //!
-14 | | //! ```standalone_crate
+14 | | //! ```standalone-crate
 15 | | //! bla
 16 | | //! ```
    | |_______^
    |
-   = help: use `standalone-crate` to compile this code block separately
+   = help: use `standalone_crate` to compile this code block separately
    = help: this code block may be skipped during testing, because unknown attributes are treated as markers for code samples written in other programming languages, unless it is also explicitly marked as `rust`
 note: the lint level is defined here
   --> $DIR/standalone-warning-2024.rs:8:9
@@ -19,19 +19,19 @@ note: the lint level is defined here
    |         ^^^^^^^^
    = note: `#[deny(rustdoc::invalid_codeblock_attributes)]` implied by `#[deny(warnings)]`
 
-error: unknown attribute `standalone_crate`
+error: unknown attribute `standalone-crate`
   --> $DIR/standalone-warning-2024.rs:10:1
    |
 10 | / //! ```standalone
 11 | | //! bla
 12 | | //! ```
 13 | | //!
-14 | | //! ```standalone_crate
+14 | | //! ```standalone-crate
 15 | | //! bla
 16 | | //! ```
    | |_______^
    |
-   = help: use `standalone-crate` to compile this code block separately
+   = help: use `standalone_crate` to compile this code block separately
    = help: this code block may be skipped during testing, because unknown attributes are treated as markers for code samples written in other programming languages, unless it is also explicitly marked as `rust`
 
 error: aborting due to 2 previous errors

tests/rustdoc-ui/doctest/standalone-warning.rs

@@ -5,6 +5,6 @@
 //! bla
 //! ```
 //!
-//! ```standalone_crate
+//! ```standalone-crate
 //! bla
 //! ```