WARNING when running with --experimental_guard_against_concurrent_changes

When running `bazel build` with `--experimental_guard_against_concurrent_changes` warnings are produced about concurrent modification and as a result not uploading the results to the cache.

```
WARNING: Skipping uploading outputs because of concurrent modifications with --experimental_guard_against_concurrent_changes enabled: /private/var/tmp/_bazel_test/29ec91ab44902ce087f81950e63441b1/execroot/_main/external/rules_oci~~oci~postgres_linux_arm64/blobs/sha256/313fe0d5de63dee76672c6f926c2da84735e135bcb657c5f619c45d5485bf7ea was modified during execution
```

Version:
```
bazel_dep(name = "rules_oci", version = "2.0.1")
```

Bazel version:
```
bazel 7.x and 8.0.x
```

Reproduce the warning with `bazel build` and `--experimental_guard_against_concurrent_changes` using rules_oci 2.0.1 on Bazel 7.x or 8.0.x. Start by tracing the reported `rules_oci~~oci~postgres_linux_arm64` blob and determine what modifies it during execution; done means the concurrent-modification warning no longer prevents cache uploads.

Written by the indexing model from the issue text.