test: deflake coverage take two (#11970)
test: deflake coverage take two (#11970)

Making the known-slow many header test slightly less slow in the hopes of reducing timeouts.

Risk Level: n/a
Testing: n/a
Docs Changes: n/a
Release Notes: n/a

Signed-off-by: Alyssa Wilk <b9253d1ec9cc3e9d2aab68d288ba3dab3452adf6@chromium.org>
lyft/envoy,lizan/envoy,lyft/envoy,envoyproxy/envoy,envoyproxy/envoy-wasm,lizan/envoy,envoyproxy/envoy-wasm,lyft/envoy,lyft/envoy,envoyproxy/envoy-wasm,lyft/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy-wasm,lizan/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy,lizan/envoy,lizan/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy,lyft/envoy,envoyproxy/envoy,envoyproxy/envoy-wasm,lizan/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy-wasm