Align Anaconda README semver example with manifest version (PR #1860 review comment)

[Copilot]

This addresses the review comment requesting the Anaconda README semver example to match the bumped manifest version (1.3.15). Scope is limited to that single comment.

• Problem scope

  • The review flagged a potential mismatch between src/anaconda/manifest.json and the concrete semver example in src/anaconda/README.md.

• Change in this PR

  • Kept the README semver example aligned with the manifest version for Anaconda (1.3.15-3), with no unrelated modifications.

• Resulting version alignment

  // src/anaconda/manifest.json
  { "version": "1.3.15" }

  <!-- src/anaconda/README.md -->
  - `mcr.microsoft.com/devcontainers/anaconda:1.3.15-3`