build(deps): bump springdoc.version from 1.6.7 to 1.6.8

Bumps `springdoc.version` from 1.6.7 to 1.6.8.

Updates `springdoc-openapi-ui` from 1.6.7 to 1.6.8
- [Release notes](https://github.com/springdoc/springdoc-openapi/releases)
- [Changelog](https://github.com/springdoc/springdoc-openapi/blob/master/CHANGELOG.md)
- [Commits](springdoc/springdoc-openapi@v1.6.7...v1.6.8)

Updates `springdoc-openapi-webmvc-core` from 1.6.7 to 1.6.8
- [Release notes](https://github.com/springdoc/springdoc-openapi/releases)
- [Changelog](https://github.com/springdoc/springdoc-openapi/blob/master/CHANGELOG.md)
- [Commits](springdoc/springdoc-openapi@v1.6.7...v1.6.8)

Updates `springdoc-openapi-kotlin` from 1.6.7 to 1.6.8
- [Release notes](https://github.com/springdoc/springdoc-openapi/releases)
- [Changelog](https://github.com/springdoc/springdoc-openapi/blob/master/CHANGELOG.md)
- [Commits](springdoc/springdoc-openapi@v1.6.7...v1.6.8)

---
updated-dependencies:
- dependency-name: org.springdoc:springdoc-openapi-ui
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.springdoc:springdoc-openapi-webmvc-core
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.springdoc:springdoc-openapi-kotlin
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

example/pom.xml

@@ -15,7 +15,7 @@
   <packaging>pom</packaging>
 
   <properties>
-    <springdoc.version>1.6.7</springdoc.version>
+    <springdoc.version>1.6.8</springdoc.version>
     <jacoco.skip>true</jacoco.skip>
     <maven.javadoc.skip>true</maven.javadoc.skip>
     <maven.sources.skip>true</maven.sources.skip>