Do not suggest adding a new lifetime bound in returned impl Trait if 'static is already specified in the signature

[estebank]

The following error

rust/src/test/ui/impl-trait/must_outlive_least_region_or_bound.stderr

Lines 37 to 53 in 0731573

	error: cannot infer an appropriate lifetime
	--> $DIR/must_outlive_least_region_or_bound.rs:12:69
	|
	LL | fn with_bound<'a>(x: &'a i32) -> impl LifetimeTrait<'a> + 'static { x }
	| -------------------------------- ^ ...but this borrow...
	| |
	| this return type evaluates to the `'static` lifetime...
	|
	note: ...can't outlive the lifetime `'a` as defined on the function body at 12:15
	--> $DIR/must_outlive_least_region_or_bound.rs:12:15
	|
	LL | fn with_bound<'a>(x: &'a i32) -> impl LifetimeTrait<'a> + 'static { x }
	| ^^
	help: you can add a bound to the return type to make it last less than `'static` and match the lifetime `'a` as defined on the function body at 12:15
	|
	LL | fn with_bound<'a>(x: &'a i32) -> impl LifetimeTrait<'a> + 'static + 'a { x }
	| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

should instead suggest changing the explicit 'static bound or not provide a suggestion at all.

Follow up to #67595.

[estebank]

Current output:

error[E0759]: `x` has an anonymous lifetime `'_` but it needs to satisfy a `'static` lifetime requirement
  --> $DIR/must_outlive_least_region_or_bound.rs:7:46
   |
LL | fn elided2(x: &i32) -> impl Copy + 'static { x }
   |               ----                           ^ ...is captured here...
   |               |
   |               this data with an anonymous lifetime `'_`...
   |
note: ...and is required to live as long as `'static` here
  --> $DIR/must_outlive_least_region_or_bound.rs:7:24
   |
LL | fn elided2(x: &i32) -> impl Copy + 'static { x }
   |                        ^^^^^^^^^^^^^^^^^^^
help: consider changing the `impl Trait`'s explicit `'static` bound to the lifetime of argument `x`
   |
LL | fn elided2(x: &i32) -> impl Copy + '_ { x }
   |                                    ^^
help: alternatively, add an explicit `'static` bound to this reference
   |
LL | fn elided2(x: &'static i32) -> impl Copy + 'static { x }
   |               ^^^^^^^^^^^^