git-annex: patch another test failure

https://git-annex.branchable.com/bugs/flaky_test_failure_add_dup/
https://hydra.nixos.org/build/306633277

similar to #438309 but applied on master due to failure for aarch64

Signed-off-by: Florian Brandes <[e-mail]>

pkgs/development/haskell-modules/configuration-common.nix

···
           # TODO(@sternenseemann): submit upstreamable patch resolving this
           # (this should be possible by also taking PREFIX into account).
           ./patches/git-annex-no-usr-prefix.patch
+          # https://git-annex.branchable.com/bugs/flaky_test_failure_add_dup/
+          (pkgs.fetchpatch {
+            name = "git-annex-workaround-for-git-2.50_bis.patch";
+            url = "https://git.joeyh.name/index.cgi/git-annex.git/patch/?id=cf449837ea9ab7687d8a157f21cad31ddf5bbfb6";
+            sha256 = "sha256-HmNJ85dLht5Hy85AUkjACnET9YLPP2MshYHsApUax+I=";
+            excludes = [
+              "doc/**"
+              "CHANGELOG"
+            ];
+          })
         ];
 
         postPatch = ''