Fixing prebuilds env

[kraenhansen]

What, How & Why?

The npm_config_realm_local_prebuilds env was set on the build jobs, but was missing from the install of the actual integration tests.

☑️ ToDos

• [ ] 📝 Changelog entry
• [x] 📝 Compatibility label is updated or copied from previous entry
• [x] 🚦 Tests
• [x] 🔀 Executed flexible sync tests locally if modifying flexible sync
• [x] 📦 Updated internal package version in consuming package.jsons (if updating internal packages)
• [x] 📱 Check the React Native/other sample apps work if necessary
• [x] 📝 Public documentation PR created or is not necessary
• [x] 💥 Breaking label has been applied or is not necessary