fixed bad file descriptor in test case

-> I noticed this, because the temporary file was not deleted
-> also this test case doesn't show up in the README.md

README.md

@@ -60,5 +60,6 @@ Testing overwrite of existing variables: ok
 Testing parsing of last line: ok
 Test loading variables from default.env file: ok
 Test .env variables override variables from default.env file: ok
+Test error message from missing .env file: ok
 $
 ```

tests/dotenv-test.sh

@@ -23,7 +23,7 @@ main() {
     assert_equal "$TEST_DEFAULT_ENVFILE" 'expected' 'Test loading variables from default.env file'
     assert_equal "$TEST_DOTENV_OVERRIDES_DEFAULT" 'expected' 'Test .env variables override variables from default.env file'
 
-    TEST_NO_ENVFILE=`DOTENV_FILE=nonexistent.env ../dotenv.sh 2>&1 >&3 3>&-` # Close stdout for this test
+    TEST_NO_ENVFILE=`DOTENV_FILE=nonexistent.env ../dotenv.sh 2>&1` # Close stdout for this test
     assert_equal "$TEST_NO_ENVFILE" "nonexistent.env file not found" 'Test error message from missing .env file'
 
     rm "$GITHUB_ENV"