Sporadic failures of `wrong number of hex digits for sha256`

# 🐞 bug report

### Description
I actually don't suspect this is a rules docker problem and may be a bazel 6.2 regression. But we started to see issues where inputs to layers that should be json files are in fact empty files. The empty files then don't load. This happens pretty infrequently 1/1000 builds. It started happening at bazel 6.2 and does not occur on bazel 5.3. I will be posting this to the bazel issue list as well.

We have seen both `wrong number of hex digits for sha256` and incorrectly formed manifest errors.

## 🔬 Minimal Reproduction

Don't have one but will follow up when I can narrow it down.

## 🔥 Exception or Error

## 🌍 Your Environment

Ubuntu 22.04

**Output of `bazel version`:**
Was occurring on bazel 6.1 and 6.2 but not on 5.3

**Rules_docker version:**