Normalize EOLs

[deivid-rodriguez]

Since #5731, checking out our repo with the default git configuration ends up with source control changes to convert EOLs of a single file:

$ GIT_CONFIG_NOSYSTEM=1 GIT_CONFIG_GLOBAL=/dev/null gh repo clone dependabot/dependabot-core foo
Cloning into 'foo'...
remote: Enumerating objects: 139226, done.
remote: Counting objects: 100% (334/334), done.
remote: Compressing objects: 100% (233/233), done.
remote: Total 139226 (delta 133), reused 251 (delta 86), pack-reused 138892
Receiving objects: 100% (139226/139226), 67.98 MiB | 20.97 MiB/s, done.
Resolving deltas: 100% (93111/93111), done.

$ git -C foo status
On branch main
Your branch is up to date with 'origin/main'.

Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git restore <file>..." to discard changes in working directory)
	modified:   nuget/spec/fixtures/nuspecs/Microsoft.Extensions.DependencyModel.nuspec

no changes added to commit (use "git add" and/or "git commit -a")

This particular file was introduced at 67baa35, but I don't see anything in that commit that suggests dos-style EOLs are relevant.

So I'm normalizing this file and removing the special case from our .gitattributes file.