spanner: test constants fail on 32-bit systems

[hongalex]

One of these spanner tests is failing on 32 bit systems. See parent issue of #14220 for more details.

# cloud.google.com/go/spanner/spansql [cloud.google.com/go/spanner/spansql.test]
src/cloud.google.com/go/spanner/spansql/parser_test.go:415:22: cannot use math.MaxInt64 (untyped int constant 9223372036854775807) as int value in argument to fmt.Sprintf (overflows)
src/cloud.google.com/go/spanner/spansql/parser_test.go:416:22: cannot use math.MinInt64 (untyped int constant -9223372036854775808) as int value in argument to fmt.Sprintf (overflows)