tests/screentest: relax pixel diffs on some tests

Use the new feature in screentest to make the retrypixels value
larger for certain tests that tend to fail.

We need the version of screentest at master because it hasn't been
tagged yet.

Change-Id: I68770f1d111895ae6c1a460599e9e6b4ee90f369
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/811800
Reviewed-by: Ethan Lee <ethanalee@google.com>
Auto-Submit: Jonathan Amsterdam <jba@google.com>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
kokoro-CI: kokoro <noreply+kokoro@google.com>

Author: jba

tests/screentest/run.sh

@@ -13,7 +13,10 @@ source devtools/docker.sh || { echo "Are you at repo root?"; exit 1; }
 # Do not truncate commands when displaying them (see runcmd in devtools/lib.sh).
 MAXWIDTH=0
 
-screentest_version=latest
+# Use the commit containing per-test retrypixels.
+# TODO: Change back to latest when this commit is under a tag
+# in x/website.
+screentest_version=1137bfaf
 
 # This should match the version we are using in devtools/docker/compose.yaml.
 chromedp_version=131.0.6778.33

tests/screentest/testcases.txt

@@ -161,6 +161,7 @@ capture viewport 540x1080
 # So do a viewport capture instead.
 test package with deprecated symbols index
 path /database/sql/driver@go1.16.3#pkg-index
+retrypixels 50
 wait {{$ready}}
 eval {{$hideElements}}
 sleep 2s
@@ -172,6 +173,7 @@ capture viewport
 # Same as the above, but for symbol doc.
 test package with deprecated symbols symbol
 path /database/sql/driver@go1.16.3#ColumnConverter
+retrypixels 50
 wait {{$ready}}
 eval {{$hideElements}}
 sleep 1s