Bump minimum Swift version to 6.0, drop 5.10 CI (#80)

### Motivation

_[Explain here the context, and why you're making that change. What is
the problem you're trying to solve.]_

### Modifications

_[Describe the modifications you've made.]_

### Result

_[After your change, what will change.]_

### Test Plan

_[Describe the steps you took, or will take, to qualify the change -
such as adjusting tests and manual testing.]_

---------

Co-authored-by: Rick Newton-Rogers <[email protected]>

Author: simonjbeaumont

.github/workflows/main.yml

@@ -14,7 +14,6 @@ jobs:
       # Disable strict concurrency checking as it intersects badly with
       # warnings-as-errors on 5.10 and later as SwiftPMs generated test manifest
       # has a non-sendable global property.
-      linux_5_10_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error"
       # TODO: Enable warnings-as-errors on 6.0.
       linux_6_0_arguments_override: "-Xswiftc -strict-concurrency=complete --explicit-target-dependency-import-check error"
       linux_6_1_arguments_override: "-Xswiftc -strict-concurrency=complete --explicit-target-dependency-import-check error"

.github/workflows/pull_request.yml

@@ -18,7 +18,6 @@ jobs:
       # Disable strict concurrency checking as it intersects badly with
       # warnings-as-errors on 5.10 and later as SwiftPMs generated test manifest
       # has a non-sendable global property.
-      linux_5_10_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error"
       # TODO: Enable warnings-as-errors on 6.0.
       linux_6_0_arguments_override: "-Xswiftc -strict-concurrency=complete --explicit-target-dependency-import-check error"
       linux_6_1_arguments_override: "-Xswiftc -strict-concurrency=complete --explicit-target-dependency-import-check error"

Package.swift

@@ -1,4 +1,4 @@
-// swift-tools-version:5.10
+// swift-tools-version:6.0
 //===----------------------------------------------------------------------===//
 //
 // This source file is part of the SwiftOpenAPIGenerator open source project

Sources/OpenAPIURLSession/BufferedStream/BufferedStream.swift

@@ -130,7 +130,7 @@ import DequeModule
 ///
 @available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *)
 @usableFromInline
-internal struct BufferedStream<Element> {
+internal struct BufferedStream<Element: Sendable> {
     @usableFromInline
     final class _Backing: Sendable {
         @usableFromInline