[Common] Fix fetching of centrality configuration in centrality study

[jesgum]

No description provided.

[github-actions]

O2 linter results: ❌ 2 errors, ⚠️ 6 warnings, 🔕 0 disabled

[alibuild]

Error while checking build/O2Physics/code-check for 5ba1c85 at 2026-07-07 15:11:

## sw/BUILD/O2Physics-code-check-latest/log
--
========== List of issues found ==========
++ echo 'Found 7 errors and 0 warnings.'
Found 7 errors and 0 warnings.
++ [[ 7 -gt 0 ]]
++ cat /sw/BUILD/a4756210e8991c08cce4e6874179631286227391/O2Physics-code-check/errors.txt
Common/Tasks/centralityStudy.cxx:49:9: error: function-like macro 'getHist' used; consider a 'constexpr' template function [cppcoreguidelines-macro-usage,-warnings-as-errors]
Common/Tasks/centralityStudy.cxx:49:54: error: macro argument should be enclosed in parentheses [bugprone-macro-parentheses,-warnings-as-errors]
Common/Tasks/centralityStudy.cxx:51:8: error: constructor does not initialize these fields: ccdb, mRunNumber, startOfRunTimestamp [cppcoreguidelines-pro-type-member-init,-warnings-as-errors]
Common/Tasks/centralityStudy.cxx:401:5: error: use auto when initializing with a template cast to avoid duplicating the type name [modernize-use-auto,-warnings-as-errors]
Common/Tasks/centralityStudy.cxx:407:7: error: use auto when initializing with a template cast to avoid duplicating the type name [modernize-use-auto,-warnings-as-errors]
Common/Tasks/centralityStudy.cxx:426:7: error: use auto when initializing with a template cast to avoid duplicating the type name [modernize-use-auto,-warnings-as-errors]
Common/Tasks/centralityStudy.cxx:565:43: error: narrowing conversion from 'float' to 'Int_t' (aka 'int') [bugprone-narrowing-conversions,-warnings-as-errors]
++ [[ 0 -gt 0 ]]
++ [[ 7 -gt 0 ]]
++ exit 1
--

Full log here.