fix CI on windows

apparently something happened with the way git 2.40 interprets commandline arguments,
amybe its an issue with git 2.40 in general.
Explicitly adding the changes (removal) seems to fix it.

Author: Byron

gix-diff/tests/fixtures/generated-archives/make_diff_repo.tar.xz

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:86d0447c83f1a348e93719f9d782784a0ced7a198ea28a94f6cccbd928d81b3d
-size 18472
+oid sha256:c37d85f4467ebe265761ffb989c0d924582e9fa5f660e1b3ad0365aca4599e84
+size 18468

gix-diff/tests/fixtures/make_diff_repo.sh

@@ -1,4 +1,5 @@
 #!/bin/bash
+set -x
 set -eu -o pipefail
 
 
@@ -20,6 +21,7 @@ echo m > f
 git commit -qam 'f modified'
 
 rm f
+git add .
 git commit -qam 'f deleted'
 
 echo m > f