[11_3_X] Fix missing LHERunInfo header bug

[colizz]

PR description:

This is a 11_3_X backport from #33831

Fix a bug that causes the header and comment not properly copied to LHERunInfoProduct from the produced LHE events. Therefore these entities are missing in LHERunInfoPruduct in the output ROOT file.

PR validation:

See #33831.

[cmsbuild]

A new Pull Request was created by @colizz (Congqiao Li) for CMSSW_11_3_X.

It involves the following packages:

GeneratorInterface/LHEInterface

@SiewYan, @mkirsano, @cmsbuild, @GurpreetSinghChahal, @agrohsje, @alberto-sanchez can you please review it and eventually sign? Thanks.
@alberto-sanchez, @mkirsano this is something you requested to watch as well.
@silviodonato, @dpiparo, @qliphy you are the release manager for this.

cms-bot commands are listed here

[SiewYan]

please test

[cmsbuild]

+1

Summary: https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-208f7f/15309/summary.html
COMMIT: 9596895
CMSSW: CMSSW_11_3_X_2021-05-25-2300/slc7_amd64_gcc900
User test area: For local testing, you can use /cvmfs/cms-ci.cern.ch/week0/cms-sw/cmssw/33841/15309/install.sh to create a dev area with all the needed externals and cmssw changes.

Comparison Summary

Summary:

• No significant changes to the logs found
• Reco comparison results: 8 differences found in the comparisons
• DQMHistoTests: Total files compared: 38
• DQMHistoTests: Total histograms compared: 2877742
• DQMHistoTests: Total failures: 12
• DQMHistoTests: Total nulls: 1
• DQMHistoTests: Total successes: 2877707
• DQMHistoTests: Total skipped: 22
• DQMHistoTests: Total Missing objects: 0
• DQMHistoSizes: Histogram memory added: -0.004 KiB( 37 files compared)
• DQMHistoSizes: changed ( 312.0 ): -0.004 KiB MessageLogger/Warnings
• Checked 160 log files, 37 edm output root files, 38 DQM output files
• TriggerResults: no differences found

[agrohsje]

+generators

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_11_3_X IBs (tests are also fine) and once validation in the development release cycle CMSSW_12_0_X is complete. This pull request will now be reviewed by the release team before it's merged. @silviodonato, @dpiparo, @qliphy (and backports should be raised in the release meeting by the corresponding L2)

[qliphy]

+1