Declare Swift 6.1 availability for TestScoping-related APIs (#927)

The `TestScoping` protocol and its related APIs have been introduced in
Swift 6.1, so this annotates their availability accordingly.

Once this PR lands, I will cherry-pick it to the `release/6.1` branch as
well.

### Checklist:

- [x] Code and documentation should follow the style of the [Style
Guide](https://github.com/apple/swift-testing/blob/main/Documentation/StyleGuide.md).
- [x] If public symbols are renamed or modified, DocC references should
be updated.

Author: stmontgomery

Sources/Testing/Testing.docc/AvailabilityStubs/Traits/SuiteTrait-scopeProvider-default-implementation-Self.md

@@ -0,0 +1,15 @@
+# ``Trait/scopeProvider(for:testCase:)-1z8kh``
+
+<!--
+This source file is part of the Swift.org open source project
+
+Copyright (c) 2025 Apple Inc. and the Swift project authors
+Licensed under Apache License v2.0 with Runtime Library Exception
+
+See https://swift.org/LICENSE.txt for license information
+See https://swift.org/CONTRIBUTORS.txt for Swift project authors
+-->
+
+@Metadata {
+  @Available(Swift, introduced: 6.1)
+}

Sources/Testing/Testing.docc/AvailabilityStubs/Traits/TestScopeProvider.md

@@ -0,0 +1,15 @@
+# ``Trait/TestScopeProvider``
+
+<!--
+This source file is part of the Swift.org open source project
+
+Copyright (c) 2025 Apple Inc. and the Swift project authors
+Licensed under Apache License v2.0 with Runtime Library Exception
+
+See https://swift.org/LICENSE.txt for license information
+See https://swift.org/CONTRIBUTORS.txt for Swift project authors
+-->
+
+@Metadata {
+  @Available(Swift, introduced: 6.1)
+}

Sources/Testing/Testing.docc/AvailabilityStubs/Traits/TestScoping-provideScope.md

@@ -0,0 +1,15 @@
+# ``TestScoping/provideScope(for:testCase:performing:)``
+
+<!--
+This source file is part of the Swift.org open source project
+
+Copyright (c) 2025 Apple Inc. and the Swift project authors
+Licensed under Apache License v2.0 with Runtime Library Exception
+
+See https://swift.org/LICENSE.txt for license information
+See https://swift.org/CONTRIBUTORS.txt for Swift project authors
+-->
+
+@Metadata {
+  @Available(Swift, introduced: 6.1)
+}

Sources/Testing/Testing.docc/AvailabilityStubs/Traits/TestScoping.md

@@ -0,0 +1,15 @@
+# ``TestScoping``
+
+<!--
+This source file is part of the Swift.org open source project
+
+Copyright (c) 2025 Apple Inc. and the Swift project authors
+Licensed under Apache License v2.0 with Runtime Library Exception
+
+See https://swift.org/LICENSE.txt for license information
+See https://swift.org/CONTRIBUTORS.txt for Swift project authors
+-->
+
+@Metadata {
+  @Available(Swift, introduced: 6.1)
+}

Sources/Testing/Testing.docc/AvailabilityStubs/Traits/Trait-scopeProvider-default-implementation-Never.md

@@ -0,0 +1,15 @@
+# ``Trait/scopeProvider(for:testCase:)-9fxg4``
+
+<!--
+This source file is part of the Swift.org open source project
+
+Copyright (c) 2025 Apple Inc. and the Swift project authors
+Licensed under Apache License v2.0 with Runtime Library Exception
+
+See https://swift.org/LICENSE.txt for license information
+See https://swift.org/CONTRIBUTORS.txt for Swift project authors
+-->
+
+@Metadata {
+  @Available(Swift, introduced: 6.1)
+}

Sources/Testing/Testing.docc/AvailabilityStubs/Traits/Trait-scopeProvider-default-implementation-Self.md

@@ -0,0 +1,15 @@
+# ``Trait/scopeProvider(for:testCase:)-inmj``
+
+<!--
+This source file is part of the Swift.org open source project
+
+Copyright (c) 2025 Apple Inc. and the Swift project authors
+Licensed under Apache License v2.0 with Runtime Library Exception
+
+See https://swift.org/LICENSE.txt for license information
+See https://swift.org/CONTRIBUTORS.txt for Swift project authors
+-->
+
+@Metadata {
+  @Available(Swift, introduced: 6.1)
+}

Sources/Testing/Testing.docc/AvailabilityStubs/Traits/Trait-scopeProvider-protocol-requirement.md

@@ -0,0 +1,15 @@
+# ``Trait/scopeProvider(for:testCase:)``
+
+<!--
+This source file is part of the Swift.org open source project
+
+Copyright (c) 2025 Apple Inc. and the Swift project authors
+Licensed under Apache License v2.0 with Runtime Library Exception
+
+See https://swift.org/LICENSE.txt for license information
+See https://swift.org/CONTRIBUTORS.txt for Swift project authors
+-->
+
+@Metadata {
+  @Available(Swift, introduced: 6.1)
+}