cmd/go: make vcstest repo scripts compatible with old Mercurial versions

The scripts added in CL 421455 passed on the TryBots, but failed on
the "-stretch" builders, which supply Mercurial 4.0
(released 2016-11-01).

Debian 9 “Stretch” has been at end-of-life since June 30, 2022, but
until we can turn down the outdated builders (golang#56414) we should keep
them passing tests.

For golang#27494.
Updates golang#56414.

Change-Id: I9df0ed452dfbfaeb1b4c0d869d02dd9ed21b3ff6
Reviewed-on: https://go-review.googlesource.com/c/go/+/445356
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/cmd/go/testdata/vcstest/hg/hgrepo1.txt

@@ -115,12 +115,26 @@ cmp stdout .hg-tags
 	# that commit lands on the 'default' branch and is not tagged as 'tip', so it
 	# seems to be mostly harmless. However, because it is nondeterministic we
 	# should avoid listing it here.
-hg branches -r 6 -r 7 -r 9
-cmp stdout .hg-branches
-
-	# Likewise, omit bookmark v3, which ends up on the nondeterministic commit.
-hg bookmarks -l master v2 v2.3.4
-cmp stdout .hg-bookmarks
+	#
+	# Unfortunately, some of our builders are still running Debian 9 “Stretch”,
+	# which shipped with a version of 'hg' that does not support 'hg branch -r'
+	# to list branches for specific versions. Although Stretch is past its
+	# end-of-life date, we need to keep the builders happy until they can be
+	# turned down (https://go.dev/issue/56414).
+hg branches
+? cmp stdout .hg-branches
+stdout 'v2\s+6:9a4f43d231ec'
+stdout 'v2.3.4\s+9:18518c07eb8e'
+stdout 'v3\s+7:a2cad8a2b1bb'
+stdout 'default\s+5:'
+
+# Likewise, bookmark v3 ends up on the nondeterministic commit.
+hg bookmarks
+? cmp stdout .hg-bookmarks
+stdout 'master\s+0:41964ddce118'
+stdout 'v2\s+3:8f49ee7a6ddc'
+stdout 'v2.3.4\s+1:88fde824ec8b'
+stdout 'v3\s+5:.*'
 
 -- .hg-branches --
 v2.3.4                         9:18518c07eb8e

src/cmd/go/testdata/vcstest/hg/vgotest1.txt

@@ -224,7 +224,7 @@ hg tags
 cmp stdout .hg-tags
 hg branches
 cmp stdout .hg-branches
-hg bookmarks -l master mybranch
+hg bookmarks
 cmp stdout .hg-bookmarks
 
 -- .hg-tags --