fetchDebianPatch: Require patch names with extensions

Otherwise the fetcher is unuseable with patches
whose filename (in Debian) doesn't end in `.patch`.

doc/builders/fetchers.chapter.md

@@ -86,7 +86,7 @@ Most other fetchers return a directory rather than a single file.
 ## `fetchDebianPatch` {#fetchdebianpatch}
 
 A wrapper around `fetchpatch`, which takes:
-- `patch` and `hash`: the patch's filename without the `.patch` suffix,
+- `patch` and `hash`: the patch's filename,
   and its hash after normalization by `fetchpatch` ;
 - `pname`: the Debian source package's name ;
 - `version`: the upstream version number ;
@@ -110,7 +110,7 @@ buildPythonPackage rec {
     (fetchDebianPatch {
       inherit pname version;
       debianRevision = "5";
-      name = "Add-quotes-to-SOAPAction-header-in-SoapClient";
+      name = "Add-quotes-to-SOAPAction-header-in-SoapClient.patch";
       hash = "sha256-xA8Wnrpr31H8wy3zHSNfezFNjUJt1HbSXn3qUMzeKc0=";
     })
   ];

pkgs/build-support/fetchdebianpatch/default.nix

@@ -1,8 +1,8 @@
 { lib, fetchpatch }:
 
 lib.makeOverridable (
-  { pname, version, debianRevision ? null, patch, hash,
-    area ? "main", name ? "${patch}.patch" }:
+  { pname, version, debianRevision ? null, area ? "main",
+    patch, name ? patch, hash }:
   let
     inherit (lib.strings) hasPrefix substring;
     prefix =
@@ -14,6 +14,6 @@ lib.makeOverridable (
     inherit name hash;
     url =
       "https://sources.debian.org/data/${area}/${prefix}/"
-      + "${pname}/${versionString}/debian/patches/${patch}.patch";
+      + "${pname}/${versionString}/debian/patches/${patch}";
   }
 )