Upstream's `.gitmodules` uses a relative submodule url (`../nvmrc.git`),
which resolves against the superproject's origin:
on a fork without its own `nvmrc` fork that is `<owner>/nvmrc`,
which 404s and fails `actions/checkout` with `submodules: true`.
Keep `submodules: true` (so a fork's own `nvmrc` is used when present),
but mark checkout `continue-on-error` and, only when it failed,
re-point the submodule at `nvm-sh/nvmrc` and update.
harden-runner runs with `egress-policy: block`, and the allow-list only included
`production.cloudflare.docker.com`. DockerHub serves image blobs from either its
Cloudflare or its CloudFront CDN; when a pull was routed to CloudFront
(`production.cloudfront.docker.com`) the connection was dropped, causing
`error pulling image configuration: ... connect: connection refused` and exit
125 in the xenial, installation_node, and fast (httpbin) suites. Allow both CDNs.
Container-based suites and the `nvm_download` httpbin check hard-fail whenever DockerHub is briefly unreachable
(observed: `dial tcp ...:443: connect: connection refused` while pulling images),
even though the change under test is fine.
This is unrelated to any test logic.
- tests-xenial / tests-installation-node: retry the `docker pull` up to 5 times before `docker run`, mirroring the existing apt-get retry
- `nvm_download` test: retry the httpbin pull and skip the auth-header checks (rather than fail) when the image cannot be pulled or run, and make cleanup tolerant of a missing container.
