Try to avoid concurrency flakiness (#1369)

(cherry picked from commit 95cc28a0ded8ed9b530266c080c5675f053c69bc)

Author: stephencelis

Sources/ComposableArchitecture/TestStore.swift

@@ -576,7 +576,9 @@
       if "\(self.file)" == "\(file)" {
         self.line = line
       }
-      await Task.megaYield()
+      // NB: Give concurrency runtime more time to kick off effects so users don't need to manually
+      //     instrument their effects.
+      await Task.megaYield(count: 20)
       return .init(rawValue: task, timeout: self.timeout)
     }
 
@@ -1044,7 +1046,7 @@
   }
 
   extension Task where Success == Never, Failure == Never {
-    static func megaYield(count: Int = 6) async {
+    static func megaYield(count: Int = 10) async {
       for _ in 1...count {
         await Task<Void, Never>.detached(priority: .low) { await Task.yield() }.value
       }