ci: Add setup script for running in Flutter "customer testing"

tools/customer-testing/setup.sh

@@ -0,0 +1,35 @@
+#!/usr/bin/env bash
+# Setup script for running Zulip's tests as part of the Flutter
+# "customer testing" suite:
+#   https://github.com/flutter/tests
+
+set -euo pipefail
+
+# Flutter's "customer testing" suite runs in two environments:
+#  * GitHub Actions for changes to the flutter/tests tree itself
+#    (which is just a registry of downstream test suites to run);
+#  * LUCI, at ci.chromium.org, for changes in Flutter.
+#
+# For background, see:
+#   https://github.com/flutter/flutter/issues/162041#issuecomment-2611129958
+
+if ! sudo -v; then
+    # In the LUCI environment sudo isn't available,
+    # but also the setup below isn't needed.  Skip it.
+    exit 0
+fi
+
+# Otherwise, assume we're in the GitHub Actions environment.
+
+
+# Install libsqlite3-dev.
+#
+# A few Zulip tests use SQLite, and so need libsqlite3.so.
+# (The actual databases involved are tiny and in-memory.)
+#
+# Both older and newer GitHub Actions images have the SQLite shared
+# library, from the libsqlite3-0 package.  But newer images
+# (ubuntu-24.04, which the ubuntu-latest alias switched to around
+# 2025-01) no longer have a symlink "libsqlite3.so" pointing to it,
+# which is part of the libsqlite3-dev package.  Install that.
+sudo apt install -y libsqlite3-dev