clippy: validator lints

[brooksprumo]

Problem

There are new nightly clippy lints in the validator crate. Refer to #34626 for more information.

warning: in a `match` scrutinee, avoid complex blocks or closures with blocks; instead, move the block or closure higher and bind it with a `let`
   --> validator/src/dashboard.rs:223:38
    |
223 |                       match async move {
    |  ______________________________________^
224 | |                         let rpc_addr = admin_client.rpc_addr().await?;
225 | |                         let start_time = admin_client.start_time().await?;
226 | |                         Ok::<_, jsonrpc_core_client::RpcError>((rpc_addr, start_time))
227 | |                     }
    | |_____________________^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#blocks_in_conditions
    = note: `#[warn(clippy::blocks_in_conditions)]` on by default

warning: `solana-validator` (lib) generated 1 warning

Summary of Changes

Fix 'em.

[codecov]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (09a94b8) 81.8% compared to head (41a3f8c) 81.8%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #34631   +/-   ##
=======================================
  Coverage    81.8%    81.8%           
=======================================
  Files         824      824           
  Lines      222260   222261    +1     
=======================================
+ Hits       181893   181901    +8     
+ Misses      40367    40360    -7