Make NMBMatcher unchecked sendable

There are 2 subclasses which are also sendable/safe to use. And no one else can make subclasses outside of Nimble, so this is tolerable

Sources/Nimble/Matchers/Matcher.swift

@@ -215,7 +215,7 @@ public typealias MatcherBlock = @Sendable (_ actualExpression: Expression<NSObje
 @available(*, deprecated, renamed: "MatcherBlock")
 public typealias PredicateBlock = MatcherBlock
 
-public class NMBMatcher: NSObject {
+public class NMBMatcher: NSObject, @unchecked Sendable {
     private let matcher: MatcherBlock
 
     public init(matcher: @escaping MatcherBlock) {