Bump lightly from 1.5.3 to 1.5.6 in /requirements

Bumps [lightly](https://github.com/lightly-ai/lightly) from 1.5.3 to 1.5.6.
- [Release notes](https://github.com/lightly-ai/lightly/releases)
- [Commits](lightly-ai/lightly@v1.5.3...v1.5.6)

---
updated-dependencies:
- dependency-name: lightly
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

requirements/required.txt

@@ -5,7 +5,7 @@ setuptools==69.5.1
 einops==0.8.0
 fiona==1.9.6
 kornia==0.7.2
-lightly==1.5.3
+lightly==1.5.6
 lightning[pytorch-extra]==2.2.4
 matplotlib==3.8.4
 numpy==1.26.4