Fix brew warnings for Spring Boot CLI

[mhalbritter]

When running brew with HOMEBREW_DEVELOPER=true, these warnings appear when running brew install spring-boot:

::warning::JARs were installed to "/home/linuxbrew/.linuxbrew/opt/spring-boot/lib". Installing JARs to "lib" can cause conflicts between packages.
For Java software, it is typically better for the formula to install to "libexec" and then symlink or wrap binaries into "bin".
See formulae 'activemq', 'jruby', etc. for examples.The offending files are:
- /home/linuxbrew/.linuxbrew/opt/spring-boot/lib/spring-boot-cli-3.4.9-SNAPSHOT.jar

When HOMEBREW_DEVELOPER is not set, those warnings are not shown.

[mhalbritter]

This is currently breaking our verification tests: https://github.com/spring-projects/spring-boot/actions/runs/17035370141/job/48287479524