Fix typo in test framework

Signed-off-by: Mats Wichmann <mats@linux.com>

Author: mwichmann

testing/framework/TestCommonTests.py

@@ -335,7 +335,7 @@ def test_file_missing(self) -> None:
         stdout = run_env.stdout()
         assert stdout == "", stdout
         stderr = run_env.stderr()
-        assert "No such file or directory:") in stderr, stderr
+        assert "No such file or directory" in stderr, stderr
 
     def test_failure(self) -> None:
         """Test must_contain():  failure"""