Fix: Use number

Author: localheinz

src/Reporter/DefaultReporter.php

@@ -158,7 +158,7 @@ private function footer(SlowTest ...$slowTests): string
         if (1 === $remainingCount) {
             return <<<'TXT'
 
-There is one additional slow test that is not listed here.
+There is 1 additional slow test that is not listed here.
 TXT;
         }
 

test/EndToEnd/Default/test.phpt

@@ -36,7 +36,7 @@ Detected 11 tests that took longer than expected.
 0.8%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Default\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDurationWithDataProvider#1
 0.7%s (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Default\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDurationWithDataProvider#0
 
-There is one additional slow test that is not listed here.
+There is 1 additional slow test that is not listed here.
 
 Time: %s, Memory: %s