Make Docker images generated by GitHub CI workflows available; minor CI fixes

[mkoeppe]

They are already tagged with meaningful names and just need to be pushed to a registry.

Now we push them to the registry provided by GitHub. Example: ​https://github.com/mkoeppe/sage/runs/604103405 created ​https://github.com/mkoeppe/sage/packages/193111

[dimpase]

will it be possible to pull an image for letting cal inspection and debugging? cool. (currently building a fedora 28 image locally...)

[mkoeppe]

Replying to dimpase:

will it be possible to pull an image for ... inspection and debugging?

Yes, that's the idea

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​e506503	Add documentation
​d6b64ba	tox-optional.yml: Push the docker images

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​06a9c39

fixup doc

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​02f86f6

tox*.yml: First try secrets.DOCKER_PKG_GITHUB_TOKEN, then secrets.GITHUB_TOKEN; ignore errors

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​00a82b0	Merge tag '9.1.rc1' into t/29530/make_docker_images_generated_by_github_ci_workflows_available
​807c2bd	Fix spelling of --downloadonly
​bd687c9	Merge branch 't/29403/ci_cygwin_yml__multi_stage_build' into t/29341/optional-test-9.1.rc0
​784abe8	ci-cygwin.yml: SAGE_FAT_BINARY=yes
​eeadb9d	.github/workflows/ci-cygwin.yml: Test more optional packages
​316c5f6	Fixup
​37c2186	Merge branch 't/29341/optional-test-9.1.rc0' into t/29530/make_docker_images_generated_by_github_ci_workflows_available

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​87210e9	.github/workflows/ci-cygwin.yml: Rebalance stages
​0d886cc	build/pkgs/pari_nftables/distros/arch.txt: Remove (package does not exist)

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​652787b

.github/workflows/tox*.yml: Make copying logs from containers more robust

[mkoeppe]

copying logs needs more work, e.g. ​https://github.com/mkoeppe/sage/runs/612694530?check_suite_focus=true displays no logs

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​2b9f531

local-{conda,homebrew}-maximal: Take packages from -standard

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​88b5aa6

tox.ini: Commit a failed build container so that logs are copied from it

[git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

​f8c6e7a

tox.ini: Commit a failed build container so that logs are copied from it

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​5c8e685	tox-optional.yml: Fix likewise
​4f4fe60	ci-cygwin.yml: Split the file so that unrelated stages do not wait

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​27c63f1

Improve docker login instructions

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​dbf461d

Merge tag '9.1.rc2' into t/29530/make_docker_images_generated_by_github_ci_workflows_available

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​163562d

Rename cygwin workflows

[dimpase]

OK, this looks nice now. I have tested just one docker image, but I trust this should be fine in general.

[mkoeppe]

Thank you!