test: Add unit test for reading exit status from a non-existent file with fallback

- Introduced a new test case in VRunnerTest to verify that the fallback value is used when the exit status file does not exist.

test/unit/groovy/ru/pulsar/jenkins/library/utils/VRunnerTest.java

@@ -109,6 +109,9 @@ class VRunnerTest {
 
         // then
         assertThat(result).isEqualTo(command);
+    }
+
+    @Test
     void readExitStatusFromFile_does_not_exist_uses_provided_fallback() {
 
         // given