tests: ignore QUIT from FTP protocol comparisons

- QUIT is not an important FTP command
- curl only sends it "best effort", meaning it might not be sent
- it is a known "flaky" thing in test output because of this

Closes #14404

tests/data/test148

@@ -28,6 +28,9 @@ ftp://%HOSTIP:%FTPPORT/attempt/to/get/this/%TESTNUMBER --ftp-create-dirs
 
 # Verify data after the test has been "shot"
 <verify>
+<strip>
+QUIT
+</strip>
 # Strip all valid kinds of PORT and EPRT that curl can send
 <strip>
 ^PORT \d{1,3},\d{1,3},\d{1,3},\d{1,3},\d{1,3},\d{1,3}