'File exists' error when building pkg_tar from srcs containing directories

### Description of the problem / feature request:

When building a pkg_tar from a filegroup defined in an external repository containing multiple files in a directory, PackgeTar throws an io exception because the directory already exists. However, the issue is not present when using `--spawn_strategy=local`.

### Bugs: what's the simplest, easiest way to reproduce this bug.

See reproduction below.

### What's the output of `bazel info release`? Happens with Bazel up through 4.x

### Have you found anything relevant by searching the web?
- I started at https://github.com/bazelbuild/rules_docker/issues/422 to find a workaround for renaming
- Then filed: https://github.com/bazelbuild/rules_docker/issues/1007

### Any other information, logs, or outputs that you want to share?

[log.txt](https://github.com/bazelbuild/bazel/files/3407651/log.txt)

Is there something that I am not understanding about how the rules should work or is this really a bug? If this is just not how the rules should work what is the solution?