Run TestWeak for fewer iterations. Five is enough reproduce #73817,
which was the motivation for this test. runtime.GC is ridiculously
slow on wasm, and not especially fast anywhere else.
Change-Id: Ieb5235d064b123cbc22a306425e385c273b54493
Reviewed-on: https://go-review.googlesource.com/c/go/+/675716 Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>