Update README.md to point to 6.2 jobs. (#1275)

This PR updates our README.md to point to 6.2 as we are no longer
targetting 6.1 on our main branch. release/6.2 continues to build for
Swift 6.1.

### 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: grynspan

README.md

@@ -103,17 +103,17 @@ Swift.
 The table below describes the current level of support that Swift Testing has
 for various platforms:
 
-| **Platform** | **CI Status (6.1)** | **CI Status (main)** | **Support Status** |
+| **Platform** | **CI Status (6.2)** | **CI Status (main)** | **Support Status** |
 |---|:-:|:-:|---|
-| **macOS** | [![Build Status](https://ci.swift.org/buildStatus/icon?job=swift-testing-main-swift-6.1-macos)](https://ci.swift.org/job/swift-testing-main-swift-6.1-macos/) | [![Build Status](https://ci.swift.org/buildStatus/icon?job=swift-testing-main-swift-main-macos)](https://ci.swift.org/view/Swift%20Packages/job/swift-testing-main-swift-main-macos/) | Supported |
+| **macOS** | [![Build Status](https://ci.swift.org/buildStatus/icon?job=swift-testing-main-swift-6.2-macos)](https://ci.swift.org/job/swift-testing-main-swift-6.2-macos/) | [![Build Status](https://ci.swift.org/buildStatus/icon?job=swift-testing-main-swift-main-macos)](https://ci.swift.org/view/Swift%20Packages/job/swift-testing-main-swift-main-macos/) | Supported |
 | **iOS** | | | Supported |
 | **watchOS** | | | Supported |
 | **tvOS** | | | Supported |
 | **visionOS** | | | Supported |
-| **Ubuntu 22.04** | [![Build Status](https://ci.swift.org/buildStatus/icon?job=swift-testing-main-swift-6.1-linux)](https://ci.swift.org/job/swift-testing-main-swift-6.1-linux/) | [![Build Status](https://ci.swift.org/buildStatus/icon?job=swift-testing-main-swift-main-linux)](https://ci.swift.org/view/Swift%20Packages/job/swift-testing-main-swift-main-linux/) | Supported |
+| **Ubuntu 22.04** | [![Build Status](https://ci.swift.org/buildStatus/icon?job=swift-testing-main-swift-6.2-linux)](https://ci.swift.org/job/swift-testing-main-swift-6.2-linux/) | [![Build Status](https://ci.swift.org/buildStatus/icon?job=swift-testing-main-swift-main-linux)](https://ci.swift.org/view/Swift%20Packages/job/swift-testing-main-swift-main-linux/) | Supported |
 | **FreeBSD** | | | Experimental |
 | **OpenBSD** | | | Experimental |
-| **Windows** | [![Build Status](https://ci-external.swift.org/buildStatus/icon?job=swift-testing-main-swift-6.1-windows)](https://ci-external.swift.org/view/all/job/swift-testing-main-swift-6.1-windows/) | [![Build Status](https://ci-external.swift.org/buildStatus/icon?job=swift-testing-main-swift-main-windows)](https://ci-external.swift.org/job/swift-testing-main-swift-main-windows/) | Supported |
+| **Windows** | [![Build Status](https://ci-external.swift.org/buildStatus/icon?job=swift-testing-main-swift-6.2-windows)](https://ci-external.swift.org/view/all/job/swift-testing-main-swift-6.2-windows/) | [![Build Status](https://ci-external.swift.org/buildStatus/icon?job=swift-testing-main-swift-main-windows)](https://ci-external.swift.org/job/swift-testing-main-swift-main-windows/) | Supported |
 | **Wasm** | | | Experimental |
 
 ### Works with XCTest