Work around https://github.com/rust-lang/rust/pull/55937

[Xanewok]

This exchanges a compilation error for a warning-but-future-error
but at least it compiles now and I'm not exactly sure how to fix it
without cloning those METHOD constants on every match (which is less
than ideal, to say the least).

[Xanewok]

Previous error:

error[E0621]: explicit lifetime required in the type of `msg`======> ] 245/246: rls(bin)
   --> src/tools/rls/src/server/mod.rs:185:21
    |
173 |       fn dispatch_message(&mut self, msg: &RawMessage) -> Result<(), jsonrpc::Error> {
    |                                           ----------- help: add explicit lifetime `'static` to the type of `msg`: `&'static server::message::RawMessage`
...
185 |                       <$n_action as LSPNotification>::METHOD => {
    |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ lifetime `'static` required
...
259 | /         match_action!(
260 | |             msg.method;
261 | |             notifications:
262 | |                 notifications::Initialized,
...   |
287 | |                 requests::CodeLensRequest;
288 | |         );
    | |__________- in this macro invocation
error: aborting due to previous error

New warning:

warning[E0597]: `msg.method` does not live long enough=============> ] 245/246: rls(bin)                                      [342/1941]
   --> src/tools/rls/src/server/mod.rs:260:13
    |
185 |                     <$n_action as LSPNotification>::METHOD => {
    |                     -------------------------------------- type annotation requires that `msg.method` is borrowed for `'static`
...
260 |             msg.method;
    |             ^^^^^^^^^^ borrowed value does not live long enough
...
290 |     }
    |     - `msg.method` dropped here while still borrowed
    |
    = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
    = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
    Finished release [optimized] target(s) in 41.03s

[Xanewok]

failures:
    test_use_statement_completion_doesnt_suggest_arguments
test result: FAILED. 12 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out

spurious failure, retrying

[Xanewok]

The underlying error/warning seems to be a bug, tracked at rust-lang/rust#57280. Gonna go ahead and merge this to fix the RLS toolstate.

cc @nrc