Allow new mismatched_lifetime_syntaxes lint (#19515)

# Objective

The new nightly lint produces [unhelpful, noisy
output](http://github.com/bevyengine/bevy/actions/runs/15491867876/job/43620116435?pr=19510)
that makes lifetimes more prominent in our library code than we
generally find helpful.

This needs to be fixed or allowed, in order to unbreak CI for every PR
in this repo.

## Solution

Blanket allow the lint at the workspace level.

## Testing

Let's see if CI passes!

Cargo.toml

@@ -72,6 +72,7 @@ allow_attributes_without_reason = "warn"
 
 [workspace.lints.rust]
 missing_docs = "warn"
+mismatched_lifetime_syntaxes = "allow"
 unexpected_cfgs = { level = "warn", check-cfg = ['cfg(docsrs_dep)'] }
 unsafe_code = "deny"
 unsafe_op_in_unsafe_fn = "warn"