Executable http_file is not runnable

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### Description of the problem / feature request:

Files downloaded using `http_file` and marked with `executable = True` cannot be run using `bazel run`.

### Bugs: what's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

Add the following to the WORKSPACE file:

```
http_file(
name = "buildifier",
executable = True,
sha256 = "069a03fc1fa46135e3f71e075696e09389344710ccee798b2722c50a2d92d55a",
urls = [
"https://github.com/bazelbuild/buildtools/releases/download/4.0.1/buildifier",
],
)
```
Run buildifier using `bazel run @buildifier//file`, and the following error occurs:

```
ERROR: Cannot run target @buildifier//file:file: Not executable
```
### What operating system are you running Bazel on?

Ubuntu 20.04 x86_64

### What's the output of `bazel info release`?

release 4.1.0

### Have you found anything relevant by searching the web?

https://github.com/bazelbuild/bazel/issues/5449