Do not try to interrupt/terminate a process if it isn't running (#5675)

Calling these on a process that isn't currently running results in

```
'NSInvalidArgumentException', reason: '*** -[NSConcreteTask terminate]: task not launched'
```

so we should check first.

rdar://96964401

(cherry picked from commit 0464fcf)

Author: neonichu

Sources/Basics/Cancellator.swift

@@ -145,13 +145,21 @@ extension TSCBasic.Process {
 #if !os(iOS) && !os(watchOS) && !os(tvOS)
 extension Foundation.Process {
     fileprivate func terminate(timeout: DispatchTime) {
+        guard self.isRunning else {
+            return
+        }
+
         // send graceful shutdown signal (SIGINT)
         self.interrupt()
 
         // start a thread to see if we need to terminate more forcibly
         let forceKillSemaphore = DispatchSemaphore(value: 0)
         let forceKillThread = TSCBasic.Thread {
             if case .timedOut = forceKillSemaphore.wait(timeout: timeout) {
+                guard self.isRunning else {
+                    return
+                }
+
                 // force kill (SIGTERM)
                 self.terminate()
             }