tests/screentest: pin screentest binary to older version

The screentest binary (golang.org/x/website/cmd/screentest) was
recently updated to use a new version of chromedp, the package that
talks to chrome in order to obtain screenshots. The new version
produces slightly different screenshots. We will eventually deal
with this when the screentest changes are finished, but for now
use an older screentest version.

Change-Id: I197501241a823f7c7ee03fab9c7312f89949af9a
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/627535
kokoro-CI: kokoro <[email protected]>
Reviewed-by: Hyang-Ah Hana Kim <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

tests/screentest/run.sh

@@ -7,6 +7,8 @@ set -e
 
 source devtools/lib.sh || { echo "Are you at repo root?"; exit 1; }
 
+screentest_version=v0.0.0-20241108174919-3a761022ad6f
+
 # This should match the version we are using in devtools/docker/compose.yaml.
 chromedp_version=97.0.4692.71
 
@@ -131,7 +133,7 @@ main() {
     dcompose up --detach chromedp
     dcompose up --detach --force-recreate frontend
     dcompose run --rm --entrypoint bash go -c "
-      go install golang.org/x/website/cmd/screentest@latest
+      go install golang.org/x/website/cmd/screentest@$screentest_version
       go run ./devtools/cmd/wait_available --timeout 120s frontend:8080 -- \
       $(echo $cmd)"
   elif [ "$env" = local ]; then
@@ -141,13 +143,13 @@ main() {
       timeout 3s bash -c -- 'while ! nc -z localhost 9222; do sleep 1; done'
     fi
     if ! command -v screentest &> /dev/null; then
-      runcmd go install golang.org/x/website/cmd/screentest@latest
+      runcmd go install golang.org/x/website/cmd/screentest@$screentest_version
     fi
     runcmd $cmd
   else
     dcompose up --detach chromedp
     dcompose run --rm --entrypoint bash go -c "
-      go install golang.org/x/website/cmd/screentest@latest
+      go install golang.org/x/website/cmd/screentest@$screentest_version
       $(echo $cmd)"
   fi
 }