diffoscope: fix build

ZHF #122042
Failing Hydra build: https://hydra.nixos.org/build/143815905

Currently the diff-check for `.mp3`-files is failing. The only reason
for that is that right now is that there are too spaces too much on the
last line[1].

[1] https://salsa.debian.org/reproducible-builds/diffoscope/-/blob/175/tests/data/mp3_expected_diff

(cherry picked from commit ea55d23cd8)

pkgs/tools/misc/diffoscope/default.nix

@@ -35,6 +35,10 @@ python3Packages.buildPythonApplication rec {
 
     # When generating manpage, use the installed version
     substituteInPlace doc/Makefile --replace "../bin" "$out/bin"
+
+    # https://salsa.debian.org/reproducible-builds/diffoscope/-/issues/258
+    substituteInPlace tests/data/mp3_expected_diff \
+      --replace "  Stream" "Stream"
   '';
 
   nativeBuildInputs = [ docutils help2man installShellFiles ];