Removed support for Swift 6.0. Now Subprocess requires Swift 6.1.0 and above

Author: iCharlesHu

Package@swift-6.0.swift

@@ -26,7 +26,7 @@ Then, adding the `Subprocess` module to your target dependencies:
 )
 ```
 
-On Swift 6.1 and above, `Subprocess` offers two [package traits](https://github.com/swiftlang/swift-evolution/blob/main/proposals/0450-swiftpm-package-traits.md):
+`Subprocess` offers two [package traits](https://github.com/swiftlang/swift-evolution/blob/main/proposals/0450-swiftpm-package-traits.md):
 
 - `SubprocessFoundation`: includes a dependency on `Foundation` and adds extensions on Foundation types like `Data`. This trait is enabled by default.
 - `SubprocessSpan`: makes Subprocess’ API, mainly `OutputProtocol`, `RawSpan` based. This trait is enabled whenever `RawSpan` is available and should only be disabled when `RawSpan` is not available.
@@ -35,7 +35,7 @@ Please find the API proposal [here](https://github.com/swiftlang/swift-foundatio
 
 ### Swift Versions
 
-The minimal supported Swift version is Swift 6.0.
+The minimal supported Swift version is **Swift 6.1**.
 
 To experiment with the `SubprocessSpan` trait, Swift 6.2 is required. Currently, you can download the Swift 6.2 toolchain (`main` development snapshot) [here](https://www.swift.org/install/macos/#development-snapshots).
 

README.md

@@ -621,10 +621,10 @@ internal struct TrackedFileDescriptor: ~Copyable {
             // if another part of the code inadvertently reuses the same file descriptor
             // number. This problem is especially concerning on Unix systems due to POSIX’s
             // guarantee of using the lowest available file descriptor number, making reuse
-            // more probable. We use `preconditionFailure` upon receiving `.badFileDescriptor`
+            // more probable. We use `fatalError` upon receiving `.badFileDescriptor`
             // to prevent accidentally closing a different file descriptor.
             guard errno != .badFileDescriptor else {
-                preconditionFailure(
+                fatalError(
                     "FileDescriptor \(fileDescriptor.rawValue) is already closed"
                 )
             }
@@ -649,10 +649,10 @@ internal struct TrackedFileDescriptor: ~Copyable {
             // if another part of the code inadvertently reuses the same file descriptor
             // number. This problem is especially concerning on Unix systems due to POSIX’s
             // guarantee of using the lowest available file descriptor number, making reuse
-            // more probable. We use `preconditionFailure` upon receiving `.badFileDescriptor`
+            // more probable. We use `fatalError` upon receiving `.badFileDescriptor`
             // to prevent accidentally closing a different file descriptor.
             guard errno != .badFileDescriptor else {
-                preconditionFailure(
+                fatalError(
                     "FileDescriptor \(fileDescriptor.rawValue) is already closed"
                 )
             }