🍒 [5.5][Concurrent] Warnings/errors should use "sendable" not "concurrent"

[ktoso]

Explanation: Some warnings were still using the "non-concurrent" wording about functions and closures. This was wording from before Sendable was a thing. This PR fixes the wording.
Risk: Low.
Reviewed By: @DougGregor
Testing: PR testing and CI on main. Tests adjusted to check for new wording.
Radar: rdar://83416205
Original PR: #39406 [Concurrent] Warnings/errors should use "sendable" not "concurrent"

[ktoso]

@swift-ci please test

[ktoso]

Windows:

  CMake will not be able to correctly generate this project.
Call Stack (most recent call first):
  CMakeLists.txt:12 (project)


-- Configuring incomplete, errors occurred!

[ktoso]

@swift-ci please test Windows

[ktoso]

@swift-ci please nominate

[ktoso]

Failures on windows unrelated:

Failed Tests (3):
  Swift(windows-x86_64) :: Interop/C/modules/print-qualified-clang-types/print-qualified-clang-types-spi.swift
  Swift(windows-x86_64) :: Interop/Cxx/operators/member-inline-module-interface.swift
  Swift-Unit :: SourceKit/SwiftLang/./SourceKitSwiftLangTests.exe/EditTest.AnnotationsAfterEdit