Replace concurrency setup with max-parallel=1 strategy in copy-workflow

[galargh]

With current concurrency setup only the first and the last matrix job was run and the rest were cancelled with Canceling since a higher priority waiting request for 'copy-*' exists.

The concurrency documentations explains this as follows:

Any previously pending job or workflow in the concurrency group will be canceled.

I think settings strategy.max-parallel: 1 in copy-workflow might do what we want it to which is to run all the matrix jobs within one copy-workflow instance sequentially: https://docs.github.com/en/actions/learn-github-actions/workflow-syntax-for-github-actions#jobsjob_idstrategymax-parallel

One thing to watch out for is if the job sequence will continue after a failure but I think it will because of the fail-fast: false setting.

[marten-seemann]

According to my understanding:

• With ~180 repos, we'll end up with 9 copy workflows.
• In each of these copy workflows, only one job is running.
  That means, we'll have a max of 9 concurrent deployments running.

[galargh]

I've verified that max-parallel: 1 + fail-fast: false work as we expect it to: https://github.com/protocol/cache-go-action/runs/4482926137?check_suite_focus=true