python3Packages.pdf2image: fix providing of poppler_utils

Due to a change in the upstream code, the previous substitution of `poppler_path` stopped
working (quietly). With this fix, it works again and will fail with an error, should another, similar
change occur.

pkgs/development/python-modules/pdf2image/default.nix

@@ -20,8 +20,10 @@ buildPythonPackage rec {
   };
 
   postPatch = ''
-    # Only replace first match in file
-    sed -i '0,/poppler_path=None/s||poppler_path="${poppler_utils}/bin"|' pdf2image/pdf2image.py
+    # replace all default values of paths to poppler_utils
+    substituteInPlace pdf2image/pdf2image.py \
+      --replace-fail 'poppler_path: Union[str, PurePath] = None' \
+                     'poppler_path: Union[str, PurePath] = "${poppler_utils}/bin"'
   '';
 
   propagatedBuildInputs = [ pillow ];