Update Bun version to fix proxy handling issues in bun install

**Describe the bug**
The current version of Bun (v1.2.11) used in claude-code-action has issues with proxy handling that cause `bun install` to hang when downloading packages, especially large packages, through a proxy. This results in random hangs at "Resolving..." or "Installing..." stages, and "ShortRead" decompression errors in Docker environments. This issue is documented in https://github.com/oven-sh/bun/issues/17793.

**To Reproduce**
Steps to reproduce the behavior:

1. Use claude-code-action with Bun v1.2.11 in an environment behind a proxy
2. Run a workflow that executes `bun install`
3. Observe the process hanging during package download or resolution
4. See errors like: `error: ShortRead decompressing "" to "..."`

**Expected behavior**
The `bun install` command should complete successfully even when running behind a proxy, without hangs or decompression errors.

**Screenshots**
N/A (Error details can be found in the linked issue: https://github.com/oven-sh/bun/issues/17793)

**Workflow yml file**
Standard claude-code-action workflow using default Bun version (v1.2.11) in environments that require proxy configuration.

**API Provider**

[x] Anthropic First-Party API (default)
[ ] AWS Bedrock
[ ] GCP Vertex

**Additional context**
- Current Bun version in claude-code-action: v1.2.11
- The proxy handling issue has been fixed in Bun via [PR #19771](https://github.com/oven-sh/bun/pull/19771) (merged on May 21, 2025)