Ensure --image-dpi on non-image produces a warning

src/ocrmypdf/_pipeline.py

@@ -129,7 +129,7 @@ def triage(input_file, output_file, options, log):
         if _pdf_guess_version(input_file):
             if options.image_dpi:
                 log.warning(
-                    "Argument --image-dpi ignored because the "
+                    "Argument --image-dpi is being ignored because the "
                     "input file is a PDF, not an image."
                 )
             # Origin file is a pdf create a symlink with pdf extension

tests/test_main.py

@@ -1125,3 +1125,14 @@ def test_fast_web_view(
     )
     with pikepdf.open(outpdf) as pdf:
         assert pdf.is_linearized == expected
+
+
+def test_image_dpi_not_image(caplog, spoof_tesseract_noop, resources, outpdf):
+    check_ocrmypdf(
+        resources / 'trivial.pdf',
+        outpdf,
+        '--image-dpi',
+        '100',
+        env=spoof_tesseract_noop,
+    )
+    assert '--image-dpi is being ignored' in caplog.text