chore: fix clippy warnings for v0.1.x (tokio-rs#2552)

## Motivation

Clippy check fails in recent CI runs in v0.1.x branch PRs, for example
this run:
https://github.com/tokio-rs/tracing/actions/runs/4641107803/jobs/8215263838


Relevant error logs:
```
error: lint `const_err` has been removed: converted into hard error, see issue #71800 <rust-lang/rust#71800> for more information
   --> tracing-core/src/lib.rs:132:5
    |
132 |     const_err,
    |     ^^^^^^^^^
    |
    = note: `-D renamed-and-removed-lints` implied by `-D warnings`


error: deref which would be done by auto-deref
   --> tracing-core/src/dispatcher.rs:371:26
    |
371 |                 return f(&*entered.current());
    |                          ^^^^^^^^^^^^^^^^^^^ help: try this: `&entered.current()`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#explicit_auto_deref
    = note: `-D clippy::explicit-auto-deref` implied by `-D warnings`


error: deref which would be done by auto-deref
   --> tracing-core/src/dispatcher.rs:393:20
    |
393 |             Some(f(&*entered.current()))
    |                    ^^^^^^^^^^^^^^^^^^^ help: try this: `&entered.current()`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#explicit_auto_deref
```

## Solution

Fix the warnings based on the suggestions for Clippy.

Author: keepsimple1

tracing-core/src/dispatcher.rs

@@ -368,7 +368,7 @@ where
     CURRENT_STATE
         .try_with(|state| {
             if let Some(entered) = state.enter() {
-                return f(&*entered.current());
+                return f(&entered.current());
             }
 
             f(&Dispatch::none())
@@ -390,7 +390,7 @@ pub fn get_current<T>(f: impl FnOnce(&Dispatch) -> T) -> Option<T> {
     CURRENT_STATE
         .try_with(|state| {
             let entered = state.enter()?;
-            Some(f(&*entered.current()))
+            Some(f(&entered.current()))
         })
         .ok()?
 }