Cover underscore in session-id parsing test

The pattern allows [A-Za-z0-9_-]+; add an underscore-containing id (abc_def-123)
to capturesMultipleSessionIds so the underscore branch of the character class is
exercised alongside the hyphenated ids.

Author: jochen-testingbot

src/test/java/testingbot/TestingBotSessionIdParsingTest.java

@@ -32,8 +32,9 @@ public void capturesPlainHexSessionId() {
     public void capturesMultipleSessionIds() {
         List<String> found = new ArrayList<>();
         TestingBotReportFactory.collectSessionIDs(
-                "TestingBotSessionID=aaa-111\nTestingBotSessionID=bbb-222", found);
-        assertThat(found).containsExactly("aaa-111", "bbb-222");
+                "TestingBotSessionID=aaa-111\nTestingBotSessionID=bbb-222\nTestingBotSessionID=abc_def-123",
+                found);
+        assertThat(found).containsExactly("aaa-111", "bbb-222", "abc_def-123");
     }
 
     @Test