Return a distinct error code if PDF/A fails

src/ocrmypdf/__main__.py

@@ -936,7 +936,7 @@ def run_pipeline():
             else:
                 msg = 'Output file is okay but is not PDF/A (seems to be {})'
                 _log.warning(msg.format(pdfa_info['conformance']))
-                return ExitCode.invalid_output_pdf
+                return ExitCode.pdfa_conversion_failed
         if not qpdf.check(options.output_file, _log):
             _log.warning('Output file: The generated PDF is INVALID')
             return ExitCode.invalid_output_pdf

src/ocrmypdf/exceptions.py

@@ -29,6 +29,7 @@ class ExitCode(IntEnum):
     child_process_error = 7
     encrypted_pdf = 8
     invalid_config = 9
+    pdfa_conversion_failed = 10
     other_error = 15
     ctrl_c = 130