🐛 fix staging CI scripts git pull failing with no tracking info

[BenoitZugmeyer]

Motivation

Follow-up to #4973: the same bare git pull bug exists in the other staging CI scripts.

Changes

• Specify the remote and branch explicitly in each git pull call across the staging CI scripts (check-squash-into-staging, check-staging-merge), matching the style already used elsewhere in the same files.

Test instructions

• Trigger the check-squash-into-staging / check-staging-merge CI jobs and confirm the git pull step no longer fails with "no tracking information".

Checklist

• Tested locally
• Tested on staging
• Added unit tests for this change.
• Added e2e/integration tests for this change.
• Updated documentation and/or relevant AGENTS.md file

[cit-pr-commenter-54b7da]

Bundles Sizes Evolution

📦 Bundle Name	Base Size	Local Size	𝚫	𝚫%	Status
Rum	181.46 KiB	181.46 KiB	0 B	0.00%	✅
Rum Profiler	8.43 KiB	8.43 KiB	0 B	0.00%	✅
Rum Recorder	22.31 KiB	22.31 KiB	0 B	0.00%	✅
Logs	57.52 KiB	57.52 KiB	0 B	0.00%	✅
Rum Salesforce	N/A	139.48 KiB	N/A	N/A	N/A
Rum Slim	139.47 KiB	139.47 KiB	0 B	0.00%	✅
Worker	22.96 KiB	22.96 KiB	0 B	0.00%	✅
Rum Shopify	N/A	202.39 KiB	N/A	N/A	N/A
Rum-shopify Profiler	N/A	8.43 KiB	N/A	N/A	N/A
Rum-shopify Recorder	N/A	3.72 KiB	N/A	N/A	N/A

[datadog-prod-us1-6]

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 77.11% (-0.01%)

_{This comment will be updated automatically if new data arrives.
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