Upgrade to Rust 1.86 and bump MSRV to 1.84 (#17171)

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## Summary

I decided to disable the new
[`needless_continue`](https://rust-lang.github.io/rust-clippy/master/index.html#needless_continue)
rule because I often found the explicit `continue` more readable over an
empty block or having to invert the condition of an other branch.


## Test Plan

`cargo test`

---------

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

crates/red_knot_python_semantic/src/suppression.rs

@@ -145,7 +145,7 @@ pub(crate) fn check_suppressions(db: &dyn Db, file: File, diagnostics: &mut Type
 fn check_unknown_rule(context: &mut CheckSuppressionsContext) {
     if context.is_lint_disabled(&UNKNOWN_RULE) {
         return;
-    };
+    }
 
     for unknown in &context.suppressions.unknown {
         match &unknown.reason {
@@ -174,7 +174,7 @@ fn check_unknown_rule(context: &mut CheckSuppressionsContext) {
                     format_args!("Unknown rule `{prefixed}`. Did you mean `{suggestion}`?"),
                 );
             }
-        };
+        }
     }
 }
 
@@ -267,7 +267,7 @@ fn check_unused_suppressions(context: &mut CheckSuppressionsContext) {
                 suppression.range,
                 format_args!("Unused `{kind}` without a code", kind = suppression.kind),
             ),
-        };
+        }
     }
 }