`cat-file --filter` is broken in 2.50?

[Dan Pristupov <dan@xxxxxxxx>]

Hi,

`cat-file --filter` stopped working in git 2.50.

```
$ git version
git version 2.47.1.windows.2

$ git cat-file --filter "HEAD:changelog.md"
<content>
```

```
$ git version
git version 2.50.0.windows.1

$ git cat-file --filter "HEAD:changelog.md"
fatal: invalid filter-spec 'HEAD:changelog.md'
```

The problem was introduced at eb83e4c64b5a3458569593c2ab0c29365f10a82f.

Then it was merged into the main branch by 
a271b05066a1fd2c3a62508d9908d6c5df14a1cb.

This seems like a bug.