test: fix test for the previous function

The unit test for the `previous` function uses an example holiday that
has a lower limit. If the randomized year is exactly the same as the
lower limit, the test fails as there is no previous date.

Increased the lower limit to avoid this situation.

Signed-off-by: Sacha Telgenhof <me@sachatelgenhof.com>

Author: stelgenhof

tests/Base/YasumiTest.php

@@ -145,7 +145,7 @@ public function testPrevious(): void
     {
         $country = 'Netherlands';
         $name = 'liberationDay';
-        $year_lower_limit = 1949;
+        $year_lower_limit = 1950;
         $year = self::numberBetween($year_lower_limit, self::YEAR_UPPER_BOUND);
 
         $holidays = Yasumi::create($country, $year);