1.5.5-cio.1: fix: use git commit instead of git branch for segment dependency

Part of: https://linear.app/customerio/issue/MBL-167/segment-dependency-currently-pointing-to-main-branch

In the iOS SDK today, with the Segment CDP SDK, we are currently specifying the version of the segment SDK as "main branch". Using a git branch as the version of a dependency poses risks, potentially leading to difficulties for customers during SDK updates and app compilation, increasing the chance of crashes or compilation issues.

This change uses a hard-coded git commit. The git commit used is the latest commit on the "main" branch.

There are pros and cons to using a git commit as the version, as specified in the ticket description. We can change to a different version such as a git tag in the future.

Note: In order for this change to be used in the iOS SDK, we need to push version 1.5.6 to the CocoaPods server and then update the iOS SDK cocoapods version to >= 1.5.6

commit-id:b1e7e3d3