Bump spring-io/spring-doc-actions from 0.0.20 to 0.0.21

Bumps [spring-io/spring-doc-actions](https://github.com/spring-io/spring-doc-actions) from 0.0.20 to 0.0.21.
- [Commits](e28269199d...4b758cb642)

---
updated-dependencies:
- dependency-name: spring-io/spring-doc-actions
  dependency-version: 0.0.21
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/update-antora-ui-spring.yml

@@ -18,7 +18,7 @@ jobs:
       matrix:
         branch: [ '1.3.x', 'main' ]
     steps:
-      - uses: spring-io/spring-doc-actions/update-antora-spring-ui@e28269199d1d27975cf7f65e16d6095c555b3cd0
+      - uses: spring-io/spring-doc-actions/update-antora-spring-ui@4b758cb6421620c108b96e4e5cd1be9f2755a3b8
         name: Update
         with:
           docs-branch: ${{ matrix.branch }}
@@ -28,7 +28,7 @@ jobs:
     runs-on: ubuntu-latest
     name: Update on docs-build
     steps:
-      - uses: spring-io/spring-doc-actions/update-antora-spring-ui@e28269199d1d27975cf7f65e16d6095c555b3cd0
+      - uses: spring-io/spring-doc-actions/update-antora-spring-ui@4b758cb6421620c108b96e4e5cd1be9f2755a3b8
         name: Update
         with:
           docs-branch: 'docs-build'