This PR prepares the release 1.15.0.

Summary by cubic

Prepares the axios 1.15.0 release by updating version metadata and syncing the exported VERSION. No functional changes.

Description

• Summary of changes
  • Bump version to 1.15.0 in package.json, package-lock.json, and bower.json.
  • Update lib/env/data.js exported VERSION to "1.15.0".
• Reasoning
  • Align package metadata and runtime version for the 1.15.0 release.
• Additional context
  • No code or API changes.

Docs

• No docs changes needed in this PR. Release notes will be handled separately.

Testing

• No tests added or modified.
• Tests are not required for version-only changes.

^{Written for commit e61021e. Summary will update on new commits.}