testdata/vcstest/bzr: fix unit test with Ubuntu 2020 LTS bzr 3.0.2

As pointed by @bcmills, upstream fixed this in 3.1.0 in breezy-team/breezy@3014386

Fixes #62620.

Change-Id: I9fa179a5293aec59496ddd401edec02e1080f1a5
GitHub-Last-Rev: 6066b05
GitHub-Pull-Request: #62652
Reviewed-on: https://go-review.googlesource.com/c/go/+/528437
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Auto-Submit: Bryan Mills <bcmills@google.com>

Author: lacombar

src/cmd/go/testdata/vcstest/bzr/hello.txt

@@ -1,6 +1,7 @@
 handle bzr
 
 env BZR_EMAIL='Russ Cox <rsc@google.com>'
+env EMAIL='Russ Cox <rsc@google.com>'
 
 bzr init-repo .