Escape percent sign in Assert::notSame message

[villfa]

This PR fixes #1662

The 3rd argument of Webmozart\Assert\Assert::notSame is passed to sprintf:

    public static function notSame($value, $expect, $message = '')
    {
        if ($expect === $value) {
            static::reportInvalidArgument(\sprintf(
                $message ?: 'Expected a value not identical to %s.',
                static::valueToString($expect)
            ));
        }
    }

See https://github.com/webmozarts/assert/blob/dc96b67/src/Assert.php#L831-L839

If we call it with a message containing %~ then PHP thows ValueError: Unknown format specifier "~".

This PR escapes the % sign to avoid this error.

[maks-rafalko]

Thank you @villfa

[maks-rafalko]

Released https://github.com/infection/infection/releases/tag/0.26.10