chore: relax lxml requirement for compatibility with older HA

[luuuis]

Prior to 2024.2.0 we can't use lxml 5.x yet.

2024-02-14 09:45:25.793 ERROR (SyncWorker_3) [homeassistant.util.package] Unable to install package lxml==5.1.0: ERROR: Cannot install lxml==5.1.0 because these package versions have conflicting dependencies.
ERROR: ResolutionImpossible: for help visit https://pip.pypa.io/en/latest/topics/dependency-resolution/#dealing-with-dependency-conflicts
2024-02-14 09:45:35.037 ERROR (SyncWorker_3) [homeassistant.util.package] Unable to install package lxml==5.1.0: ERROR: Cannot install lxml==5.1.0 because these package versions have conflicting dependencies.
ERROR: ResolutionImpossible: for help visit https://pip.pypa.io/en/latest/topics/dependency-resolution/#dealing-with-dependency-conflicts
2024-02-14 09:45:43.460 ERROR (SyncWorker_3) [homeassistant.util.package] Unable to install package lxml==5.1.0: ERROR: Cannot install lxml==5.1.0 because these package versions have conflicting dependencies.
ERROR: ResolutionImpossible: for help visit https://pip.pypa.io/en/latest/topics/dependency-resolution/#dealing-with-dependency-conflicts
2024-02-14 09:45:43.462 ERROR (MainThread) [homeassistant.setup] Setup failed for custom integration 'wibeee': Requirements for wibeee not found: ['lxml==5.1.0'].