Update Swift NIO checkout to 2.78.0

[d-ronnqvist]

This updates the Swift NIO version in utils/update_checkout/update-checkout-config.json for the main branch to 2.78.0—which is the first release which contains apple/swift-nio#2969.

This enables projects like Swift-DocC to avoid warning about capturing non-sendable types when working with NIO types like EventLoopPromise.

[d-ronnqvist]

swiftlang/swift-docc#1146
@swift-ci test

[d-ronnqvist]

I don't see how this failure would be caused by the NIO update:

Failed Tests (1):
  Swift(iphonesimulator-x86_64) :: Interop/Cxx/objc-correctness/appkit-uikit.swift


Testing Time: 1648.14s

Total Discovered Tests: 18927
  Unsupported      :  1357 (7.17%)
  Passed           : 17524 (92.59%)
  Expectedly Failed:    45 (0.24%)
  Failed           :     1 (0.01%)

[d-ronnqvist]

swiftlang/swift-docc#1146
@swift-ci test

[d-ronnqvist]

This however, seems caused by this version update:

/swift-nio/Sources/NIOPosix/DatagramVectorReadManager.swift:43:28: error: initializer 'init(msg_hdr:msg_len:)' is not available due to missing import of defining module 'CNIODarwin'
 14 | import CNIOLinux
 15 | import NIOCore
 16 | 
    | `- note: add import of module 'CNIODarwin'
 17 | /// An object that manages issuing vector reads for datagram channels.
 18 | ///
    :
 41 | 
 42 |             self.messageVector = .allocateAndInitialize(
 43 |                 repeating: MMsgHdr(msg_hdr: msghdr(), msg_len: 0),
    |                            `- error: initializer 'init(msg_hdr:msg_len:)' is not available due to missing import of defining module 'CNIODarwin'
 44 |                 count: newValue
 45 |             )