[5.9] Fix macOS build issues (#419)

* Potential workaround for a CI issue (#404)

* Potential workaround for a CI issue

The macOS CI does not seem to work with Xcode 14.2 as superior, hitting

```
error: Error Domain=NSCocoaErrorDomain Code=4 "The file "swiftpm" doesn't exist." UserInfo={NSFilePath=/Users/ec2-user/jenkins/workspace/pr-swift-tools-support-core-macos/branch-main/swift-tools-support-core/Utilities/ci.xcworkspace/xcshareddata/swiftpm, NSUnderlyingError=0x600000a5a310 {Error Domain=NSPOSIXErrorDomain Code=2 "No such file or directory"}}
```

I have a theory that this is triggered by us using a workspace that does not contain a resolved file, but that case works for me with SwiftPM 5.9 locally, so not sure.

* Use python 3

macOS 12 comes with updated python.

* Try empty resolved file (#417)

We only added the resolved file as a workaround, we may not need any concrete pins for that.

---------

Co-authored-by: Boris Bügling <[email protected]>

Author: MaxDesiatov

Tests/TSCBasicTests/ProcessTests.swift

@@ -466,12 +466,7 @@ class ProcessTests: XCTestCase {
 
 fileprivate extension Process {
     private static func env() -> [String:String] {
-        var env = ProcessEnv.vars
-        #if os(macOS)
-        // Many of these tests use Python which might not be in the default `PATH` when running these tests from Xcode.
-        env["PATH"] = "\(env["PATH"] ?? ""):/usr/local/bin"
-        #endif
-        return env
+        return ProcessEnv.vars
     }
 
     private static func script(_ name: String) -> String {

Tests/TSCBasicTests/processInputs/deadlock-if-blocking-io

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 import sys
 

Tests/TSCBasicTests/processInputs/in-to-out

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 import sys
 

Tests/TSCBasicTests/processInputs/long-stdout-stderr

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 import sys
 

Tests/TSCBasicTests/processInputs/simple-stdout-stderr

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 import sys