Run release triggered main pipeline integration tests at concurrency 1

[paolino]

Changes

• Add j parameter to just command to control concurrency of integration tests
• Add buildkite controls for the parameter
• Set concurrency to 1 when building for release pipeline

Issue

#5045

Notes

• proof https://buildkite.com/cardano-foundation/cardano-wallet/builds/9740/canvas?jid=019595ce-b39a-4e87-8a56-d5f3480ea152#019595ce-b39a-4e87-8a56-d5f3480ea152/181-188

[abailly]

As you mentioned in your message, it's unclear whether running tests concurrently is the issue.
I had a Quick Look at the source code for the particular failure.
It seems to me we are trying to reimplement a function that already exists in the process package, namely readCreateProcessWithExitCode, albeit without taking care of the possibility of SIGPIPE being triggered, nor of the ordering of operations: Perhaps reading the pipe after closing the input stream leads to the underlying process to terminate and therefore the pipe to be closed?
I haven't tested it, but adding a delay after the hClose might surface the issue more consistently.