Refactor file exitence check to _upload_file

Moves the logic of checking for files existence into the method
`_upload_file` as it was handling the process of uploading the
file.

Changed the error message to be more appropriate to the raised
error.

Refactored to write error via `self._io`.

Author: 1nF0rmed

src/poetry/publishing/uploader.py

@@ -212,10 +212,6 @@ def _upload(
         self, session: requests.Session, url: str, dry_run: Optional[bool] = False
     ) -> None:
         for file in self.files:
-            if not file.is_file():
-                raise UploadError(
-                    "Wheel or Tar files associated with the Project Package do not exist"
-                )
 
             self._upload_file(session, url, file, dry_run)
 
@@ -228,6 +224,10 @@ def _upload_file(
     ) -> None:
         from cleo.ui.progress_bar import ProgressBar
 
+        if not file.is_file():
+            self._io.write_error(f"Archive ({file}) does not exist", True)
+            raise UploadError(f"Archive ({file}) does not exist")
+
         data = self.post_data(file)
         data.update(
             {

tests/publishing/test_uploader.py

@@ -68,6 +68,4 @@ def test_uploader_properly_handles_file_not_existing(mocker, http, uploader):
     with pytest.raises(UploadError) as e:
         uploader.upload("https://foo.com")
 
-    assert "Wheel or Tar files associated with the Project Package do not exist" == str(
-        e.value
-    )
+    assert f"Archive ({uploader.files[0]}) does not exist" == str(e.value)