Chart release occuring concurrently causes conflicts

[mgoerens]

Example of two PRs running the Release job at the same time, resulting in a conflict (failed push) for one of them:

• Add verification report for remote-active-worker-ubi 3.51.8 charts#1985 (success)
• Add verification report for nonamesec-ubi 3.51.8 charts#1986 (failed)

We currently use https://github.com/softprops/turnstyle for this use case, but that apparently did not successfully block in that case. We should investigate.

Github has now a way to control concurrency on a job or workflow level but this misses a crucial feature for our use case discussed here