chore(deps): update actions/cache action to v6 (#1454)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [actions/cache](https://redirect.github.com/actions/cache) | action |
major | `v5` → `v6` |

---

### Release Notes

<details>
<summary>actions/cache (actions/cache)</summary>

###
[`v6.0.0`](https://redirect.github.com/actions/cache/releases/tag/v6.0.0)

[Compare
Source](https://redirect.github.com/actions/cache/compare/v6.0.0...v6.0.0)

#### What's Changed

- Update packages, migrate to ESM by
[@&#8203;Samirat](https://redirect.github.com/Samirat) in
[#&#8203;1760](https://redirect.github.com/actions/cache/pull/1760)

**Full Changelog**:
<actions/cache@v5...v6.0.0>

###
[`v6`](https://redirect.github.com/actions/cache/compare/v5.0.5...v6.0.0)

[Compare
Source](https://redirect.github.com/actions/cache/compare/v5.0.5...v6.0.0)

</details>

---

### Configuration

📅 **Schedule**: (UTC)

- Branch creation
  - At any time (no schedule defined)
- Automerge
  - At any time (no schedule defined)

🚦 **Automerge**: Disabled by config. Please merge this manually once you
are satisfied.

♻ **Rebasing**: Whenever PR is behind base branch, or you tick the
rebase/retry checkbox.

🔕 **Ignore**: Close this PR and you won't be reminded about this update
again.

---

- [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check
this box

---

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View the [repository job
log](https://developer.mend.io/github/openapi-generators/openapi-python-client).

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.github/workflows/checks.yml

@@ -27,7 +27,7 @@ jobs:
         shell: bash
 
       - name: Cache dependencies
-        uses: actions/cache@v5
+        uses: actions/cache@v6
         with:
           path: .venv
           key: ${{ runner.os }}-${{ steps.get_python_version.outputs.python_version }}-dependencies-${{ hashFiles('**/pdm.lock') }}
@@ -86,7 +86,7 @@ jobs:
         shell: bash
 
       - name: Cache dependencies
-        uses: actions/cache@v5
+        uses: actions/cache@v6
         with:
           path: .venv
           key: ${{ runner.os }}-${{ steps.get_python_version.outputs.python_version }}-min-dependencies-${{ hashFiles('**/pdm.lock') }}
@@ -168,7 +168,7 @@ jobs:
         id: get_python_version
         run: echo "python_version=$(python --version)" >> $GITHUB_OUTPUT
       - name: Cache Generated Client Dependencies
-        uses: actions/cache@v5
+        uses: actions/cache@v6
         with:
           path: integration-tests/.venv
           key: ${{ runner.os }}-${{ steps.get_python_version.outputs.python_version }}-integration-dependencies-${{ hashFiles('integration-tests/pdm*.lock') }}