Fix some warnings shown in nightly

[ameknite]

Objective

Fix warnings:

• #[warn(clippy::needless_pass_by_ref_mut)]
• #[warn(elided_lifetimes_in_associated_constant)]

Solution

• Remove mut
• add &'static

Errors

warning: this argument is a mutable reference, but not used mutably
   --> crates/bevy_hierarchy/src/child_builder.rs:672:31
    |
672 |     fn assert_children(world: &mut World, parent: Entity, children: Option<&[Entity]>) {
    |                               ^^^^^^^^^^ help: consider changing to: `&World`
    |
    = note: this is cfg-gated and may require further changes
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_pass_by_ref_mut
    = note: `#[warn(clippy::needless_pass_by_ref_mut)]` on by default

warning: `&` without an explicit lifetime name cannot be used here
   --> examples/shader/post_processing.rs:120:21
    |
120 |     pub const NAME: &str = "post_process";
    |                     ^
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #115010 <https://github.com/rust-lang/rust/issues/115010>
    = note: `#[warn(elided_lifetimes_in_associated_constant)]` on by default
help: use the `'static` lifetime
    |
120 |     pub const NAME: &'static str = "post_process";
    |                      +++++++