testing: add TB.Setenv

For #41260 and #46688.

Change-Id: I6f42742cc3234a90003136ae8798a6b0e1291788
Reviewed-on: https://go-review.googlesource.com/c/go/+/326790
Trust: Russ Cox <[email protected]>
Run-TryBot: Russ Cox <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>

Author: rsc

api/go1.17.txt

@@ -181,6 +181,7 @@ pkg syscall (windows-amd64), type SysProcAttr struct, AdditionalInheritedHandles
 pkg syscall (windows-amd64), type SysProcAttr struct, ParentProcess Handle
 pkg testing, method (*B) Setenv(string, string)
 pkg testing, method (*T) Setenv(string, string)
+pkg testing, type TB interface, Setenv(string, string)
 pkg text/template/parse, const SkipFuncCheck = 2
 pkg text/template/parse, const SkipFuncCheck Mode
 pkg time, const Layout = "01/02 03:04:05PM '06 -0700"

src/testing/testing.go

@@ -644,6 +644,7 @@ type TB interface {
 	Log(args ...interface{})
 	Logf(format string, args ...interface{})
 	Name() string
+	Setenv(key, value string)
 	Skip(args ...interface{})
 	SkipNow()
 	Skipf(format string, args ...interface{})