Fix semver hazard in S3 stalled stream protection test (#3541)

Merging #3485 uncovered a semver hazard in the S3 stalled stream
protection test due to a subtle (but intentional) change in grace period
behavior for stalled streams. That semver hazard was going to cause the
SDK release to fail, so #3485 was reverted, and this PR modifies the
test so that it will pass with both versions of stalled stream
protection as a temporary measure. Once this PR is merged and released,
then the new stalled stream protection can be merged again.

I tested this by updating the runtime-versioner in #3540 so that I could
patch the currently released SDK with these test changes in place, with
a local copy of smithy-rs that has the new stalled stream protection
implementation. I ran all the tests across all the services in this
configuration to verify this was the only hazard that will be hit.

----

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aws/sdk/integration-tests/s3/tests/stalled-stream-protection.rs

@@ -229,8 +229,14 @@ async fn test_stalled_stream_protection_for_downloads_is_enabled_by_default() {
         err.to_string(),
         "minimum throughput was specified at 1 B/s, but throughput of 0 B/s was observed"
     );
-    // 1s check interval + 5s grace period
-    assert_eq!(start.elapsed().as_secs(), 6);
+    // 5s grace period
+    // TODO(https://github.com/smithy-lang/smithy-rs/issues/3510): Currently comparing against 5 and 6 due to
+    // the behavior change in #3485. Once that feature/fix is released, this should be changed to only check for 5.
+    let elapsed_secs = start.elapsed().as_secs();
+    assert!(
+        elapsed_secs == 5 || elapsed_secs == 6,
+        "elapsed secs should be 5 or 6, but was {elapsed_secs}"
+    )
 }
 
 async fn start_faulty_download_server() -> (impl Future<Output = ()>, SocketAddr) {