Bug: sometimes gitlab api fails with `ValidationError: "id" is required`

[mordamax]

Example: paritytech/cumulus#2220 (comment)

@mordamax Command "$PIPELINE_SCRIPTS_DIR/commands/bench/bench.sh" all has finished. Result:

ValidationError: "id" is required
ValidationError: "id" is required
{"message":{"base":["Reference not found"]}}

[mordamax]

Still reproduces here: paritytech/cumulus#2344 (comment)

Found out that the check of branch existence is made with retries, but then the pipeline calls right away, which is naive, since the pipeline is more likely to delay its creation so the fix would be add retriable and/or preventive delay prior calling it