Drop --continue-at from curl call

It is incompatible with -J and done automatically. See [1].

[1] https://gitlab.archlinux.org/archlinux/archlinux-docker/-/jobs/34434#L72
11 jobs for master in 3 minutes and 24 seconds (queued for 6 seconds)
Status Name Job ID Coverage
  .Pre
passed get_version #34608

00:00:10

 
  Cleanup
passed cleanup #34609
secure

00:00:24

 
  Lint
passed lint #34610

00:00:28

 
  Rootfs
passed rootfs:secure: [base-devel] #34612
secure

00:01:59

passed rootfs:secure: [base] #34611
secure

00:02:04

 
  Image
failed image:build:secure: [base-devel] #34614
secure

00:00:14

failed image:build:secure: [base] #34613
secure

00:00:14

 
  Test
skipped test:base #34615
skipped test:base-devel #34616
 
  Release
skipped release #34617
secure
 
  Publish
skipped publish #34618
 
Name Stage Failure
failed
image:build:secure: [base-devel] Image
INFO[0003] SHELL ["/bin/bash", "-c"]                    
INFO[0003] RUN ROOTFS="$(curl -sOJL -w "%{filename_effective}" file:///base-devel.tar.xz)" && sha256sum -c <<< "e9cfeeeaa3e7a6b0c32d582931ab747a2573f67d30730de0bb219cf2e8acb58c base-devel.tar.xz" && mkdir /rootfs && tar -C /rootfs --extract --file "${ROOTFS}"
INFO[0003] cmd: /bin/bash
INFO[0003] args: [-c ROOTFS="$(curl -sOJL -w "%{filename_effective}" file:///base-devel.tar.xz)" && sha256sum -c <<< "e9cfeeeaa3e7a6b0c32d582931ab747a2573f67d30730de0bb219cf2e8acb58c base-devel.tar.xz" && mkdir /rootfs && tar -C /rootfs --extract --file "${ROOTFS}"]
INFO[0003] Running: [/bin/bash -c ROOTFS="$(curl -sOJL -w "%{filename_effective}" file:///base-devel.tar.xz)" && sha256sum -c <<< "e9cfeeeaa3e7a6b0c32d582931ab747a2573f67d30730de0bb219cf2e8acb58c base-devel.tar.xz" && mkdir /rootfs && tar -C /rootfs --extract --file "${ROOTFS}"]
sha256sum: WARNING: 1 of 1 computed checksums did NOT match
base-devel.tar.xz: FAILED
error building image: error building stage: failed to execute command: waiting for process to exit: exit status 1
Cleaning up file based variables
ERROR: Job failed: exit code 1
failed
image:build:secure: [base] Image
INFO[0003] SHELL ["/bin/bash", "-c"]                    
INFO[0003] RUN ROOTFS="$(curl -sOJL -w "%{filename_effective}" file:///base.tar.xz)" && sha256sum -c <<< "5237279ff61d802c48d3b591764f682744d7fee3532b60c818df27d8729a140b base.tar.xz" && mkdir /rootfs && tar -C /rootfs --extract --file "${ROOTFS}"
INFO[0003] cmd: /bin/bash
INFO[0003] args: [-c ROOTFS="$(curl -sOJL -w "%{filename_effective}" file:///base.tar.xz)" && sha256sum -c <<< "5237279ff61d802c48d3b591764f682744d7fee3532b60c818df27d8729a140b base.tar.xz" && mkdir /rootfs && tar -C /rootfs --extract --file "${ROOTFS}"]
INFO[0003] Running: [/bin/bash -c ROOTFS="$(curl -sOJL -w "%{filename_effective}" file:///base.tar.xz)" && sha256sum -c <<< "5237279ff61d802c48d3b591764f682744d7fee3532b60c818df27d8729a140b base.tar.xz" && mkdir /rootfs && tar -C /rootfs --extract --file "${ROOTFS}"]
base.tar.xz: FAILED
sha256sum: WARNING: 1 of 1 computed checksums did NOT match
error building image: error building stage: failed to execute command: waiting for process to exit: exit status 1
Cleaning up file based variables
ERROR: Job failed: exit code 1