[SRU] libreoffice 7.5.9 for lunar

[Impact]

 * LibreOffice 7.5.9 is in its ninth and last bugfix release of the 7.5 line:
     https://wiki.documentfoundation.org/ReleasePlan/7.5#7.5.9_release

 * Version 7.5.8 is currently released in lunar. For a list of fixed bugs compared to 7.5.8 see the list of bugs fixed in the release candidates of 7.5.9 (that's a total of ? bugs):
     https://wiki.documentfoundation.org/Releases/7.5.9/RC1#List_of_fixed_bugs
     https://wiki.documentfoundation.org/Releases/7.5.9/RC2#List_of_fixed_bugs

     7.5.9 RC2 is identical to the 7.5.9 release

 * Given the nature of the project, the complexity of the codebase and the high level of quality assurance upstream, it is preferable to SRU a minor release rather than cherry-pick selected bug fixes.

[Testing]

 * Upstream testing. Bugs fixed upstream typically include unit/regression tests, and the release itself is extensively exercised (both in an automated manner and manually).

  * A recent set of upstream's automated jenkins testing can be found here:
    https://ci.libreoffice.org/job/gerrit_75/1776/

  * More information about the upstream QA testing can be found here:
    * Automated tests
      https://wiki.documentfoundation.org/QA/Testing/Automated_Tests
    * Automated UI tests
      https://wiki.documentfoundation.org/Development/UITests
    * Regression tests
      https://wiki.documentfoundation.org/QA/Testing/Regression_Tests
    * Feature tests
      https://wiki.documentfoundation.org/QA/Testing/Feature_Tests

 * Launchpad testing. The libreoffice packages include autopkgtests that were run and verified as passing.
    Tested build can be found at https://launchpad.net/~ricotz/+archive/ubuntu/ppa/+sourcepub/15402714/+listing-archive-extra
    * [amd64] https://autopkgtest.ubuntu.com/results/autopkgtest-lunar-ricotz-ppa/lunar/amd64/libr/libreoffice/20231130_032215_7d344@/log.gz
    * [arm64] https://autopkgtest.ubuntu.com/results/autopkgtest-lunar-ricotz-ppa/lunar/arm64/libr/libreoffice/20231130_110658_1779c@/log.gz
    * [armhf] ... (autopkgtests infra problems on this arch)
    * [ppc64el] https://autopkgtest.ubuntu.com/results/autopkgtest-lunar-ricotz-ppa/lunar/ppc64el/libr/libreoffice/20231129_180258_07169@/log.gz
    * [riscv64] not available
    * [s390x] https://autopkgtest.ubuntu.com/results/autopkgtest-lunar-ricotz-ppa/lunar/s390x/libr/libreoffice/20231130_024056_ac67e@/log.gz
 * General smoke testing of all the applications in the office suite were carried out by going through the manual testplan as documented by: https://wiki.ubuntu.com/Process/Merges/TestPlans/libreoffice

[Regression Potential]

 * A minor release with a total of ? bug fixes always carries the potential for introducing regressions, even though it is a bugfix-only release, meaning that no new features were added, and no existing features were removed.

 * A combination of autopkgtests and careful smoke testing as described above should provide reasonable confidence that no regressions sneaked in.