Error saving the cache

## Orb version: 1.8.0

## What happened:

The step "Process cache save" (for the `rust/build` command) failed with this error:
```
+ '[' -n '' ']'
+ mkdir -p /tmp/cargo_tmp
+ cp -r /home/circleci/.cargo /tmp/cargo_tmp/
cp: cannot create regular file '/tmp/cargo_tmp/.cargo/git/checkouts/some-redacted-crate/XXXXXXX/.git/objects/pack/pack-redacted.idx': Permission denied
cp: cannot create regular file '/tmp/cargo_tmp/.cargo/git/checkouts/some-redacted-crate/XXXXXXX/.git/objects/pack/pack-redacted.pack': Permission denied

Exited with code exit status 1
```

and the step "Process cache restore" (for the `rust/test` command) failed with this error:
```
+ '[' -d /tmp/cargo_tmp ']'
+ echo 'Cache directory found'
Cache directory found
+ '[' -n '' ']'
+ rm -r /home/circleci/.cargo
rm: remove write-protected regular file '/home/circleci/.cargo/git/db/some-redacted-crate/objects/pack/pack-redacted.idx'? rm: remove write-protected regular file '/home/circleci/.cargo/git/db/some-redacted-crate/objects/pack/pack-redacted.pack'? rm: cannot remove '/home/circleci/.cargo/git/db/some-redacted-crate/objects/pack': Directory not empty
```

I had to use this config to workaround these issues:
```yaml
- rust/build:
with_cache: false

- rust/test:
with_cache: false
```

## Expected behavior:

The command without disabling cache should work out of the box.

## Additional Information:

It is likely that this issue only happens for Rust projects with dependencies.

No source files or tests are named. Start by locating the cache handling used by the rust/build and rust/test commands, then reproduce the failure with a Rust dependency cache. Done means both commands work with caching enabled and no longer require with_cache: false.

Written by the indexing model from the issue text.