ci: enable code coverage for main branch for better reports

[levibostian]

I noticed in a recent PR that changed no source code files, code coverage reports in the PR were weird. I realized it's because PRs compare it's code coverage against the main branch's code coverage. Which, at this time, do not get uploaded.

This PR modifies the CI to generate code coverage on the main branch so PR code coverage reports are more accurate.

[github-actions]

Sample app builds 📱

Below you will find the list of the latest versions of the sample apps. It's recommended to always download the latest builds of the sample apps to accurately test the pull request.

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• CocoaPods-FCM: levi/codecov-main-coverage (1695988759)
• APN-UIKit: levi/codecov-main-coverage (1695988717)

[codecov]

Codecov Report

Merging #389 (f469d0a) into main (9dad7f3) will increase coverage by 3.36%.
Report is 124 commits behind head on main.
The diff coverage is 34.07%.

@@            Coverage Diff             @@
##             main     #389      +/-   ##
==========================================
+ Coverage   56.11%   59.48%   +3.36%     
==========================================
  Files         103      119      +16     
  Lines        1153     4556    +3403     
==========================================
+ Hits          647     2710    +2063     
- Misses        506     1846    +1340     

Files	Coverage Δ
...s/Common/Background Queue/ApiSyncQueueRunner.swift	86.11% <ø> (+2.77%)	⬆️
...ces/Common/Background Queue/QueueQueryRunner.swift	100.00% <100.00%> (ø)
.../Common/Background Queue/QueueRequestManager.swift	100.00% <100.00%> (ø)
...rces/Common/Background Queue/QueueRunRequest.swift	95.62% <100.00%> (+5.62%)	⬆️
...ask Data/DeletePushNotificationQueueTaskData.swift	100.00% <100.00%> (ø)
...Queue/Task Data/IdentifyProfileQueueTaskData.swift	100.00% <100.00%> (ø)
...k Data/RegisterPushNotificationQueueTaskData.swift	100.00% <100.00%> (ø)
...ound Queue/Task Data/TrackEventQueueTaskData.swift	100.00% <100.00%> (ø)
...ces/Common/Background Queue/Type/QueueStatus.swift	100.00% <ø> (ø)
...urces/Common/Background Queue/Type/QueueTask.swift	100.00% <ø> (ø)
... and 81 more

... and 45 files with indirect coverage changes