fix(windows): keep stdin open for conpty processes (#8885)

### Description

I forgot that ConPTY behaves differently than Linux-style
psuedoterminals. If `stdin` is closed on a process hooked up to a
ConPTY, then the process will immediately end.

### Testing Instructions

Cut a canary and test it on a Windows machine.

crates/turborepo-lib/src/process/mod.rs

@@ -60,6 +60,19 @@ impl ProcessManager {
         let use_pty = !cfg!(windows) && atty::is(atty::Stream::Stdout);
         Self::new(use_pty)
     }
+
+    /// Returns whether children will be spawned attached to a pseudoterminal
+    pub fn use_pty(&self) -> bool {
+        self.use_pty
+    }
+
+    /// Returns whether or not closing a child's stdin will result in it
+    /// immediately exiting.
+    pub fn closing_stdin_ends_process(&self) -> bool {
+        // Processes spawned hooked up to ConPTY on Windows will immediately exit
+        // if their stdin is closed. We avoid closing stdin in this case.
+        cfg!(windows) && self.use_pty
+    }
 }
 
 impl ProcessManager {

crates/turborepo-lib/src/task_graph/visitor.rs

@@ -956,7 +956,7 @@ impl ExecContext {
         // Even if user does not have the TUI and cannot interact with a task, we keep
         // stdin open for persistent tasks as some programs will shut down if stdin is
         // closed.
-        if !self.takes_input {
+        if !self.takes_input && !self.manager.closing_stdin_ends_process() {
             process.stdin();
         }