build: add a retry on git push in merge-pr.sh

[coriolinus]

Github sometimes takes a few seconds to figure out that after a force-push to a branch, we are still allowed to merge it to main. So this does a sleep/retry, once, in the event that the first push fails.

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PR Submission Checklist for internal contributors

• The PR Title
  • conforms to the style of semantic commits messages¹ supported in Wire's Github Workflow²
  • contains a reference JIRA issue number like SQPIT-764
  • answers the question: If merged, this PR will: ... ³

1. https://sparkbox.com/foundry/semantic_commit_messages
2. https://github.com/wireapp/.github#usage
3. E.g. feat(conversation-list): Sort conversations by most emojis in the title #SQPIT-764.

[github-actions]

Bencher Report

Branch	prgn/build/delay-in-merge-pr
Testbed	ubuntu-latest

Click to view all benchmark results

Benchmark	Latency	milliseconds (ms)
Commit add f(group size)/cs1/mem/1002	📈 view plot 🚷 view threshold	19.36
Commit add f(group size)/cs1/mem/2	📈 view plot 🚷 view threshold	7.29
Commit add f(group size)/cs1/mem/202	📈 view plot 🚷 view threshold	9.67
Commit add f(group size)/cs1/mem/402	📈 view plot 🚷 view threshold	12.10
Commit add f(group size)/cs1/mem/602	📈 view plot 🚷 view threshold	15.31
Commit add f(group size)/cs1/mem/802	📈 view plot 🚷 view threshold	17.41
Commit add f(number clients)/cs1/mem/1002	📈 view plot 🚷 view threshold	981.68
Commit add f(number clients)/cs1/mem/2	📈 view plot 🚷 view threshold	7.35
Commit add f(number clients)/cs1/mem/202	📈 view plot 🚷 view threshold	84.75
Commit add f(number clients)/cs1/mem/402	📈 view plot 🚷 view threshold	219.67
Commit add f(number clients)/cs1/mem/602	📈 view plot 🚷 view threshold	425.84
Commit add f(number clients)/cs1/mem/802	📈 view plot 🚷 view threshold	671.29
Commit pending proposals f(group size)/cs1/mem/1002	📈 view plot 🚷 view threshold	116.06
Commit pending proposals f(group size)/cs1/mem/2	📈 view plot 🚷 view threshold	28.68
Commit pending proposals f(group size)/cs1/mem/202	📈 view plot 🚷 view threshold	46.37
Commit pending proposals f(group size)/cs1/mem/402	📈 view plot 🚷 view threshold	61.32
Commit pending proposals f(group size)/cs1/mem/602	📈 view plot 🚷 view threshold	80.43
Commit pending proposals f(group size)/cs1/mem/802	📈 view plot 🚷 view threshold	94.82
Commit pending proposals f(pending size)/cs1/mem/1	📈 view plot 🚷 view threshold	19.11
Commit pending proposals f(pending size)/cs1/mem/101	📈 view plot 🚷 view threshold	115.60
Commit pending proposals f(pending size)/cs1/mem/21	📈 view plot 🚷 view threshold	35.94
Commit pending proposals f(pending size)/cs1/mem/41	📈 view plot 🚷 view threshold	56.74
Commit pending proposals f(pending size)/cs1/mem/61	📈 view plot 🚷 view threshold	75.34
Commit pending proposals f(pending size)/cs1/mem/81	📈 view plot 🚷 view threshold	95.55
Commit remove f(group size)/cs1/mem/1002	📈 view plot 🚷 view threshold	28.68
Commit remove f(group size)/cs1/mem/2	📈 view plot 🚷 view threshold	7.14
Commit remove f(group size)/cs1/mem/202	📈 view plot 🚷 view threshold	9.08
Commit remove f(group size)/cs1/mem/402	📈 view plot 🚷 view threshold	12.30
Commit remove f(group size)/cs1/mem/602	📈 view plot 🚷 view threshold	17.87
Commit remove f(group size)/cs1/mem/802	📈 view plot 🚷 view threshold	22.32
Commit remove f(number clients)/cs1/mem/1002	📈 view plot 🚷 view threshold	30.97
Commit remove f(number clients)/cs1/mem/2	📈 view plot 🚷 view threshold	137.87
Commit remove f(number clients)/cs1/mem/202	📈 view plot 🚷 view threshold	115.66
Commit remove f(number clients)/cs1/mem/402	📈 view plot 🚷 view threshold	93.88
Commit remove f(number clients)/cs1/mem/602	📈 view plot 🚷 view threshold	71.95
Commit remove f(number clients)/cs1/mem/802	📈 view plot 🚷 view threshold	51.27
Commit update f(group size)/cs1/mem/1002	📈 view plot 🚷 view threshold	138.05
Commit update f(group size)/cs1/mem/2	📈 view plot 🚷 view threshold	7.38
Commit update f(group size)/cs1/mem/202	📈 view plot 🚷 view threshold	34.15
Commit update f(group size)/cs1/mem/402	📈 view plot 🚷 view threshold	60.05
Commit update f(group size)/cs1/mem/602	📈 view plot 🚷 view threshold	87.10
Commit update f(group size)/cs1/mem/802	📈 view plot 🚷 view threshold	112.50

🐰 View full continuous benchmarking report in Bencher