Bump spring-boot.version from 2.3.12.RELEASE to 2.6.1

Bumps `spring-boot.version` from 2.3.12.RELEASE to 2.6.1.

Updates `spring-boot-starter-parent` from 2.3.12.RELEASE to 2.6.1
- [Release notes](https://github.com/spring-projects/spring-boot/releases)
- [Commits](https://github.com/spring-projects/spring-boot/compare/v2.3.12.RELEASE...v2.6.1)

Updates `spring-boot-maven-plugin` from 2.3.12.RELEASE to 2.6.1
- [Release notes](https://github.com/spring-projects/spring-boot/releases)
- [Commits](https://github.com/spring-projects/spring-boot/compare/v2.3.12.RELEASE...v2.6.1

)

---
updated-dependencies:
- dependency-name: org.springframework.boot:spring-boot-starter-parent
  dependency-type: direct:production
  update-type: version-update:semver-minor
- dependency-name: org.springframework.boot:spring-boot-maven-plugin
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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