fix: sanitize branch names for semantic-release prerelease

[abueide]

Summary

Fixes the semantic-release configuration to prevent branch names with underscores from breaking releases.

Problem

The wildcard branch config ({ name: '*', prerelease: true }) uses the raw branch name as the prerelease identifier. Branch names with underscores (e.g., leanplum_plugin_integration) violate the SemVer specification which only allows [0-9A-Za-z-] in prerelease identifiers.

This caused the beta channel release to fail with:

EPRERELEASEBRANCH A pre-release branch configuration is invalid in the `branches` configuration.

Solution

Changed the wildcard branch config to use a fixed prerelease identifier ('beta') instead of the branch name:

{ name: '*', prerelease: 'beta' }

This ensures:

• All feature/fix branches publish as beta prereleases (e.g., 1.2.3-beta.1)
• SemVer compliance regardless of branch naming
• Releases work even with branches containing underscores

Test Plan

• Verified configuration syntax
• Test beta release from a branch with underscores
• Test beta release from the fix/ios-zero-second-sessions branch

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