chore: ignore 'session shutdown' yamux error in tests (coder#17964)

Fixes flake seen here: https://github.com/coder/coder/actions/runs/15154327939/job/42606133069?pr=17960

Error log dropped when the dRPC server is being shut down right as we are (re)dialing.

Author: EdwardAngert

testutil/logger.go

@@ -5,6 +5,7 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/hashicorp/yamux"
 	"golang.org/x/xerrors"
 
 	"cdr.dev/slog"
@@ -24,6 +25,11 @@ func IgnoreLoggedError(entry slog.SinkEntry) bool {
 	if !ok {
 		return false
 	}
+	// Yamux sessions get shut down when we are shutting down tests, so ignoring
+	// them should reduce flakiness.
+	if xerrors.Is(err, yamux.ErrSessionShutdown) {
+		return true
+	}
 	// 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