testing: mention in docs for Logf that a final newline is added if needed
testing: mention in docs for Logf that a final newline is added if needed

Fixes #16423

Change-Id: I9635db295be4d356d427adadd309084e16c4582f
Reviewed-on: https://go-review.googlesource.com/31255
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

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