chore: add standard test logger ignoring db canceled (#15556)

Refactors our use of `slogtest` to instantiate a "standard logger" across most of our tests.  This standard logger incorporates https://github.com/coder/slog/pull/217 to also ignore database query canceled errors by default, which are a source of low-severity flakes.

Any test that has set non-default `slogtest.Options` is left alone. In particular, `coderdtest` defaults to ignoring all errors. We might consider revisiting that decision now that we have better tools to target the really common flaky Error logs on shutdown.

testutil/logger.go

@@ -0,0 +1,47 @@
+package testutil
+
+import (
+	"context"
+	"strings"
+	"testing"
+
+	"golang.org/x/xerrors"
+
+	"cdr.dev/slog"
+	"cdr.dev/slog/sloggers/slogtest"
+)
+
+// Logger returns a "standard" testing logger, with debug level and common flaky
+// errors ignored.
+func Logger(t testing.TB) slog.Logger {
+	return slogtest.Make(
+		t, &slogtest.Options{IgnoreErrorFn: IgnoreLoggedError},
+	).Leveled(slog.LevelDebug)
+}
+
+func IgnoreLoggedError(entry slog.SinkEntry) bool {
+	err, ok := slogtest.FindFirstError(entry)
+	if !ok {
+		return false
+	}
+	// Canceled queries usually happen when we're shutting down tests, and so
+	// ignoring them should reduce flakiness.  This also includes
+	// context.Canceled and context.DeadlineExceeded errors, even if they are
+	// not part of a query.
+	return isQueryCanceledError(err)
+}
+
+// isQueryCanceledError checks if the error is due to a query being canceled. This reproduces
+// database.IsQueryCanceledError, but is reimplemented here to avoid importing the database package,
+// which would result in import loops. We also use string matching on the error PostgreSQL returns
+// to us, rather than the pq error type, because we don't want testutil, which is imported in lots
+// of places to import lib/pq, which we have our own fork of.
+func isQueryCanceledError(err error) bool {
+	if xerrors.Is(err, context.Canceled) || xerrors.Is(err, context.DeadlineExceeded) {
+		return true
+	}
+	if strings.Contains(err.Error(), "canceling statement due to user request") {
+		return true
+	}
+	return false
+}