fix flaky async test

internal/asyncassertion/async_assertion_test.go

diff --git a/internal/asyncassertion/async_assertion_test.go b/internal/asyncassertion/async_assertion_test.go
index 3b58272..95e4e82 100644
--- a/internal/asyncassertion/async_assertion_test.go
+++ b/internal/asyncassertion/async_assertion_test.go
@@ -66,7 +66,8 @@
 
 				a.Should(HaveLen(11), "My description %d", 2)
 
-				Ω(arr).Should(HaveLen(10))
+				Ω(len(arr)).Should(BeNumerically(">", 8))
+				Ω(len(arr)).Should(BeNumerically("<=", 10))
 				Ω(failureMessage).Should(ContainSubstring("Timed out after"))
 				Ω(failureMessage).Should(ContainSubstring("<[]int | len:10"), "Should pass the correct value to the matcher message formatter.")
 				Ω(failureMessage).Should(ContainSubstring("My description 2"))