Update 6.2.1 related package dependency versions

The release/6.2.1 branch has dependencies on release/6.2 branch, these need to be updated.

Specifically.

```
.package(url: "https://github.com/swiftlang/swift-llbuild.git", branch: "release/6.2"),
.package(url: "https://github.com/swiftlang/swift-tools-support-core.git", branch: "release/6.2"),

```