fix: racy double creation of docker tag

[luc-hiverge]

When running:

$ hive create exp -f hive.yaml noop-

I frequently run into the following error:

Image build command: docker buildx build --platform linux/amd64 --file /tmp/tmpix44g6d5/repo/Dockerfile --tag temp-image:latest --load /tmp/tmpix44g6d5/repo
Image build command: docker buildx build --platform linux/amd64 --file /tmp/tmp94_lihwo/Dockerfile --tag gcr.io/runsandbox-449400/random-fitness:1936839 --load --push /tmp/tmp94_lihwo
Build STDERR:
...

#12 [8/8] RUN rsync -a /app/repo/ /app/.backup/
#12 CACHED

#13 exporting to image
#13 exporting layers done
#13 exporting manifest sha256:03a5775f0be41fe32d8ed74eb40116c9aeeeb5519a13bff0d0143df72736f2fb done
#13 exporting config sha256:c6e2c2e11af13ef90214a0b26dcd24427affb3abcc0cf70472ce7c02c8416568 done
#13 exporting attestation manifest sha256:b4987b28c9281b4974ae96f59de59ab57cc15e75b8cea1b2e04385f93d19c662 0.1s done
#13 exporting manifest list sha256:02606d3040576dd32bf1c44b97da170ff673f5fc703246208b32572d8f600eba 0.0s done
#13 naming to gcr.io/runsandbox-449400/random-fitness:1936839 done
#13 unpacking to gcr.io/runsandbox-449400/random-fitness:1936839 done
#13 CANCELED

#14 exporting to image
#14 exporting layers done
#14 exporting manifest sha256:03a5775f0be41fe32d8ed74eb40116c9aeeeb5519a13bff0d0143df72736f2fb done
#14 exporting config sha256:c6e2c2e11af13ef90214a0b26dcd24427affb3abcc0cf70472ce7c02c8416568 done
#14 exporting attestation manifest sha256:b4987b28c9281b4974ae96f59de59ab57cc15e75b8cea1b2e04385f93d19c662 0.1s done
#14 exporting manifest list sha256:02606d3040576dd32bf1c44b97da170ff673f5fc703246208b32572d8f600eba 0.0s done
#14 naming to gcr.io/runsandbox-449400/random-fitness:1936839 done
#14 ERROR: image "gcr.io/runsandbox-449400/random-fitness:1936839": already exists

The documentation claims that --load is only valid for single-platform builds. Since, we're doing multi-platform build, I suspect this flag might be invalid.

Removing --load is highly effective at stopping the issue, especially in the version shown in the first commit. The second version I've run a few times and is too succeeds (but it's identical to the previous version in my setup).

[luc-hiverge]

/kind fix

[luc-hiverge]

/kind bug

[ky-hiverge]

/lgtm
/approve

I add this for some reason before, but forgot it. Merge for now.