testing: fix flakey test on plan9
testing: fix flakey test on plan9

allow for more than 0.00s.

Fixes #15149

Change-Id: I1d428a9b3c9bb3d1db8682c53b86e44cecc1dde1
Reviewed-on: https://go-review.googlesource.com/21602
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
Run-TryBot: Marcel van Lohuizen <a22d082192f3ccf984644a4f482781f4c2d65180@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

derekmarcotte/go,codestation/go,josharian/go,CAFxX/go,polyverse-security/go,vanloswang/go,akutz/go,vsekhar/elastic-go,vsekhar/elastic-go,Cofyc/go,polyverse-security/go,suncycheng/go,ImJasonH/go,theif519/go,codestation/go,akutz/go,Cofyc/go,linux-on-ibm-z/go,suncycheng/go,momchil-velikov/go,goodlang/good,derekmarcotte/go,ImJasonH/go,linux-on-ibm-z/go,derekmarcotte/go,codestation/go,derekmarcotte/go,ImJasonH/go,goodlang/good,goodlang/good,vsekhar/elastic-go,suncycheng/go,ImJasonH/go,christopher-henderson/Go,Cofyc/go,CAFxX/go,vsekhar/elastic-go,josharian/go,golang/go,akutz/go,goodlang/good,josharian/go,akutz/go,vanloswang/go,golang/go,vsekhar/elastic-go,ganboing/go-esx,derekmarcotte/go,vanloswang/go,4ad/go,nawawi/go,akutz/go,suncycheng/go,josharian/go,golang/go,Cofyc/go,josharian/go,codestation/go,theif519/go,CAFxX/go,ImJasonH/go,Cofyc/go,linux-on-ibm-z/go,cloudflare/go,Cofyc/go,momchil-velikov/go,ImJasonH/go,linux-on-ibm-z/go,polyverse-security/go,vsekhar/elastic-go,vsekhar/elastic-go,ganboing/go-esx,suncycheng/go,CAFxX/go,momchil-velikov/go,ganboing/go-esx,codestation/go,4ad/go,vanloswang/go,theif519/go,suncycheng/go,theif519/go,momchil-velikov/go,Cofyc/go,ImJasonH/go,ganboing/go-esx,momchil-velikov/go,Cofyc/go,nawawi/go,akutz/go,4ad/go,ganboing/go-esx,golang/go,cloudflare/go,derekmarcotte/go,momchil-velikov/go,cloudflare/go,polyverse-security/go,nawawi/go,4ad/go,theif519/go,4ad/go,vanloswang/go,akutz/go,4ad/go,josharian/go,cloudflare/go,linux-on-ibm-z/go,ImJasonH/go,cloudflare/go,cloudflare/go,goodlang/good,vanloswang/go,4ad/go,josharian/go,nawawi/go,suncycheng/go,nawawi/go,4ad/go,goodlang/good,linux-on-ibm-z/go,theif519/go,polyverse-security/go,derekmarcotte/go,cloudflare/go,polyverse-security/go,golang/go,theif519/go,nawawi/go,linux-on-ibm-z/go,akutz/go,vanloswang/go,CAFxX/go,CAFxX/go,golang/go,codestation/go,theif519/go,golang/go,ganboing/go-esx,vanloswang/go,cloudflare/go,derekmarcotte/go,golang/go,ganboing/go-esx,momchil-velikov/go,nawawi/go,suncycheng/go,momchil-velikov/go,polyverse-security/go,vsekhar/elastic-go,codestation/go,CAFxX/go,goodlang/good,ganboing/go-esx,josharian/go,nawawi/go,CAFxX/go,goodlang/good,linux-on-ibm-z/go,codestation/go,polyverse-security/go