Prevent pulling if another "podman pull" is in progress

This is a workaround to deal with
https://github.com/containers/podman/issues/24527, once that's fixed
this can be dropped, but might still be useful to not pull multiple
images at once, which I think might duplicate some work. Without this
the memory usage during pulls is currently too much to handle.

.forgejo/workflows/build-image.yaml

@@ -11,6 +11,7 @@ jobs:
       - run:  podman login -u ${{ vars.REGISTRY_USERNAME }} -p ${{ secrets.REGISTRY_PASSWORD }} ${{ vars.REGISTRY_DOMAIN }}
       # base
       - run:  mkdir cache
+      - run:  while [[ $(pgrep -f '^podman pull') ]]; do sleep 2; done
       - run:  podman pull quay.io/fedora-ostree-desktops/kinoite:41
       - run:  podman build . -f Dockerfile.kde --no-cache --pull=never -v ${PWD}/cache:/var/cache/libdnf5:Z --squash -t ${{ vars.REGISTRY_DOMAIN }}/ver4a/onc-kde:main
       - run:  podman push --compression-format=zstd --compression-level=${{ vars.COMPRESSION_LEVEL }} ${{ vars.REGISTRY_DOMAIN }}/ver4a/onc-kde:main ${{ vars.REGISTRY_DOMAIN }}/ver4a/onc-kde:main
@@ -33,6 +34,7 @@ jobs:
       - run:  podman login -u ${{ vars.REGISTRY_USERNAME }} -p ${{ secrets.REGISTRY_PASSWORD }} ${{ vars.REGISTRY_DOMAIN }}
       # base
       - run:  mkdir cache
+      - run:  while [[ $(pgrep -f '^podman pull') ]]; do sleep 2; done
       - run:  podman pull quay.io/fedora-ostree-desktops/silverblue:41
       - run:  podman build . -f Dockerfile.gnome --no-cache --pull=never -v ${PWD}/cache:/var/cache/libdnf5:Z --squash -t ${{ vars.REGISTRY_DOMAIN }}/ver4a/onc-gnome:main
       - run:  podman push --compression-format=zstd --compression-level=${{ vars.COMPRESSION_LEVEL }} ${{ vars.REGISTRY_DOMAIN }}/ver4a/onc-gnome:main ${{ vars.REGISTRY_DOMAIN }}/ver4a/onc-gnome:main