chore(deps): update actions/cache action to v4 (#570)

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This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [actions/cache](https://togithub.com/actions/cache) | action | major |
`v3` -> `v4` |

---

### Release Notes

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

### [`v4`](https://togithub.com/actions/cache/compare/v3...v4)

[Compare Source](https://togithub.com/actions/cache/compare/v3...v4)

</details>

---

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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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.github/workflows/diff-check.yml

@@ -28,7 +28,7 @@ jobs:
 
       # Install openapi-generator-cli
       - run: echo "OPENAPI_GENERATOR_VERSION=6.6.0" >> $GITHUB_ENV
-      - uses: actions/cache@v3
+      - uses: actions/cache@v4
         id: openapi-generator-cache
         env:
           cache-name: openapi-generator-cache

.github/workflows/php-checks.yml

@@ -31,7 +31,7 @@ jobs:
 
       - name: Install openapi-generator-cli
         run: echo "OPENAPI_GENERATOR_VERSION=6.6.0" >> $GITHUB_ENV
-      - uses: actions/cache@v3
+      - uses: actions/cache@v4
         id: openapi-generator-cache
         env:
           cache-name: openapi-generator-cache
@@ -56,7 +56,7 @@ jobs:
         run: |
           echo "dir=$(composer config cache-files-dir)" >> $GITHUB_OUTPUT
 
-      - uses: actions/cache@v3
+      - uses: actions/cache@v4
         with:
           path: ${{ steps.composer-cache.outputs.dir }}
           key: ${{ runner.os }}-php-${{ matrix.php }}-${{ hashFiles('**/composer.lock') }}