chore: update Ruby version from 3.1 to 3.4 in workflows and README (#22)

**Requirements**

- [ ] I have added test coverage for new or changed functionality
- [x] I have followed the repository's [pull request submission
guidelines](../blob/main/CONTRIBUTING.md#submitting-pull-requests)
- [x] I have validated my changes against all supported platform
versions

**Related issues**

- [Failing CI
job](https://github.com/launchdarkly/openfeature-ruby-server/actions/runs/23911603051/job/69734764063)
— `Bundler found conflicting requirements for the Ruby version` when
running with Ruby 3.1.7.

**Describe the solution you've provided**

The `openfeature-sdk ~> 0.6.0` dependency requires Ruby >= 3.4, and the
gemspec's `required_ruby_version` was already updated to `>= 3.4` in
#16. However, three workflows and the README still referenced Ruby 3.1:

1. **`release-please.yml`** — used `ruby-version: 3.1` for the CI step
during release → updated to `3.4`
2. **`manual-publish.yml`** — used `ruby-version: 3.1` for the
build-and-test step → updated to `3.4`
3. **`manual-publish-docs.yml`** — used `ruby-version: 3.1` for
`setup-ruby` → updated to `3.4`
4. **`README.md`** — stated "Ruby 3.1 and above" → updated to "Ruby 3.4
and above"

**Describe alternatives you've considered**

- **Widening `openfeature-sdk` to `~> 0.4`** to restore Ruby 3.1
support: Rejected per reviewer feedback — the intent is to keep
`openfeature-sdk ~> 0.6.0` and require Ruby 3.4+.

**Additional context**

The `ci.yml` workflow was already updated to Ruby 3.4 in #16; only the
release/publish workflows were missed.

**Human review checklist**

- [ ] Verify no other files still reference Ruby 3.1 (e.g. grep for
`3.1` across `.github/`)

Link to Devin session:
https://app.devin.ai/sessions/0a8e066ab2c447618bcefa0be007594a
Requested by: @kinyoklion

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Low risk: updates only CI/release GitHub Actions configuration and
README text, with no runtime code changes. Main risk is CI/publish
failures if Ruby 3.4 environment assumptions differ from prior runs.
> 
> **Overview**
> Aligns automation and documentation with the project’s Ruby 3.4+
requirement by updating GitHub Actions workflows to run build/test,
release, and docs publishing using Ruby `3.4` instead of `3.1`.
> 
> Updates the README to state support for Ruby `3.4` and above.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
53daf5e. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

---------

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

Author: kinyoklion

.github/workflows/manual-publish-docs.yml

@@ -13,7 +13,7 @@ jobs:
 
       - uses: ruby/setup-ruby@3ff19f5e2baf30647122352b96108b1fbe250c64 # v1.299.0
         with:
-          ruby-version: 3.1
+          ruby-version: 3.4
 
       - uses: ./.github/actions/build-docs
 

.github/workflows/manual-publish.yml

@@ -28,7 +28,7 @@ jobs:
         name: Build and Test
         uses: ./.github/actions/ci
         with:
-          ruby-version: 3.1
+          ruby-version: 3.4
 
       - id: publish
         name: Publish Package

.github/workflows/release-please.yml

@@ -32,7 +32,7 @@ jobs:
       - uses: ./.github/actions/ci
         if: ${{ steps.release.outputs.releases_created == 'true' }}
         with:
-          ruby-version: 3.1
+          ruby-version: 3.4
 
       - uses: ./.github/actions/build-docs
         if: ${{ steps.release.outputs.releases_created == 'true' }}

README.md

@@ -24,7 +24,7 @@ This provider is designed primarily for use in multi-user systems such as web se
 
 ## Supported Ruby versions
 
-This version of the LaunchDarkly provider works with Ruby 3.1 and above.
+This version of the LaunchDarkly provider works with Ruby 3.4 and above.
 
 ## Getting started