[PWGLF] lambdapolarization.cxx: replace rapidity with eta

[jikim1290]

replace rapidity with eta

[github-actions]

O2 linter results: ❌ 0 errors, ⚠️ 20 warnings, 🔕 0 disabled

[alibuild]

Error while checking build/O2Physics/code-check for 0cd03d4 at 2026-07-20 11:19:

## sw/BUILD/O2Physics-code-check-latest/log
--
========== List of issues found ==========
++ echo 'Found 2 errors and 0 warnings.'
Found 2 errors and 0 warnings.
++ [[ 2 -gt 0 ]]
++ cat /sw/BUILD/cf9d223d7830b674245ba4cd1e920fc8d03b2dde/O2Physics-code-check/errors.txt
PWGLF/Tasks/Strangeness/lambdaTwoPartPolarization.cxx:541:37: error: repeated branch body in conditional chain [bugprone-branch-clone,-warnings-as-errors]
PWGLF/Tasks/Strangeness/lambdaTwoPartPolarization.cxx:573:37: error: repeated branch body in conditional chain [bugprone-branch-clone,-warnings-as-errors]
++ [[ 0 -gt 0 ]]
++ [[ 2 -gt 0 ]]
++ exit 1
--

Full log here.

[vkucera]

The PR title contains no information about which code is affected by the changes.
@jikim1290 Please follow the contribution guidelines.
@lhusova Please enforce the contribution guidelines.

[jikim1290]

@Luca610 I have modified the title of this PR and could you please merge it? thanks!