[CI]: buildkit `Internal: not found`

### Description

This is happening regularly. Seen on experimental #3303 twice in the same run (rootless, if that matters).

Attached is a copy of the logs from tests relying on `build`.

Intuition (wild guess, actually) suggest this might be related to containerd delete / garbage-collection, and could possibly be a buildkitd issue.

### Steps to reproduce the issue

1.
2.
3.

### Describe the results you received and expected

```
=== FAIL: cmd/nerdctl/container TestRunCopyingUpInitialContentsOnDockerfileVolume (0.62s)
testutil.go:655: buildkitHost="unix:///run/user/1001/buildkit-nerdctl-test/buildkitd.sock"
container_run_mount_linux_test.go:182: assertion failed: res.ExitCode is not exitCode:
Command: /usr/local/bin/nerdctl --namespace=nerdctl-test build -t nerdctl-testruncopyingupinitialcontentsondockerfilevolume /tmp/TestRunCopyingUpInitialContentsOnDockerfileVolume3738922107/001
ExitCode: 1
Error: exit status 1
Stdout:
Stderr: #1 [internal] load build definition from Dockerfile
#1 transferring dockerfile: 188B done
#1 DONE 0.0s

#2 [internal] load metadata for ghcr.io/stargz-containers/alpine:3.13-org
#2 DONE 0.1s

#3 [internal] load .dockerignore
#3 transferring context: 2B done
#3 DONE 0.0s

#4 [1/2] FROM ghcr.io/stargz-containers/alpine:3.13-org@sha256:ec14c7992a97fc11425907e908340c6c3d6ff602f5f13d899e6b7027c9b4133a
#4 resolve ghcr.io/stargz-containers/alpine:3.13-org@sha256:ec14c7992a97fc11425907e908340c6c3d6ff602f5f13d899e6b7027c9b4133a 0.0s done
#4 CACHED

#5 [2/2] RUN mkdir -p /mnt && echo hi > /mnt/initial_file
#5 DONE 0.2s

#6 exporting to image
#6 exporting layers 0.0s done
#6 exporting manifest sha256:c54c31e481be28beb9b5893fd6569dc20c123705ea4246aa49ef503e993c96f9 done
#6 exporting config sha256:b60e26ee3e57f3fb47e4bf798dd06502add47433c3d668007a0d8d14d11502ae done
#6 naming to docker.io/library/nerdctl-testruncopyingupinitialcontentsondockerfilevolume:latest done
#6 unpacking to docker.io/library/nerdctl-testruncopyingupinitialcontentsondockerfilevolume:latest 0.0s done
#6 DONE 0.1s
error: failed to solve: Internal: not found

=== FAIL: cmd/nerdctl/container TestRunCopyingUpInitialContentsOnVolume (0.48s)
testutil.go:655: buildkitHost="unix:///run/user/1001/buildkit-nerdctl-test/buildkitd.sock"
container_run_mount_linux_test.go:154: assertion failed: res.ExitCode is not exitCode:
Command: /usr/local/bin/nerdctl --namespace=nerdctl-test build -t nerdctl-testruncopyingupinitialcontentsonvolume /tmp/TestRunCopyingUpInitialContentsOnVolume1393391841/001
ExitCode: 1
Error: exit status 1
Stdout:
Stderr: #1 [1/2] FROM ghcr.io/stargz-containers/alpine:3.13-org@sha256:ec14c7992a97fc11425907e908340c6c3d6ff602f5f13d899e6b7027c9b4133a
#1 resolve ghcr.io/stargz-containers/alpine:3.13-org@sha256:ec14c7992a97fc11425907e908340c6c3d6ff602f5f13d899e6b7027c9b4133a 0.0s done
#1 CACHED

#2 [internal] load build definition from Dockerfile
#2 transferring dockerfile: 176B done
#2 DONE 0.0s

#3 [2/2] RUN mkdir -p /mnt && echo hi > /mnt/initial_file
#3 DONE 0.2s

#4 [internal] load metadata for ghcr.io/stargz-containers/alpine:3.13-org
#4 DONE 0.1s

#5 [internal] load .dockerignore
#5 transferring context: 2B done
#5 DONE 0.0s

#6 exporting to image
#6 exporting layers done
#6 exporting manifest sha256:20fe0bd0c4692c355a83232ef93987b9a638cefe724ccb7593d21897e3cdd437 done
#6 exporting config sha256:478c4aac618d55bb333a7c16c8c0c6d69db6958fee358d562ffedd1232e6719c done
#6 naming to docker.io/library/nerdctl-testruncopyingupinitialcontentsonvolume:latest done
#6 unpacking to docker.io/library/nerdctl-testruncopyingupinitialcontentsonvolume:latest 0.0s done
#6 DONE 0.0s
error: failed to solve: Internal: not found
```

### What version of nerdctl are you using?

main

### Are you using a variant of nerdctl? (e.g., Rancher Desktop)

None

### Host information

_No response_