[PWGEM] Change from sliceByCached back to sliceBy

[ikantak]

change sliceByCached back to sliceBy in QC and QCMC task due to error with fIndexEMEvents

[alibuild]

Error while checking build/O2Physics/o2 for e38be4e at 2026-02-23 13:31:

## sw/BUILD/O2Physics-latest/log
[FATAL] Unhandled o2::framework::runtime_error reached the top of main of /sw/BUILD/7c382c879c81a38aedc24c1ddf67a787890dc6c8/O2Physics/stage/bin/o2-analysis-em-pcm-qc, device shutting down. Reason: Preslice not valid: table "V0PhotonsKF_001" (or join based on it) does not have column "fIndexEMEvents"
[FATAL] Unhandled o2::framework::runtime_error reached the top of main of /sw/BUILD/7c382c879c81a38aedc24c1ddf67a787890dc6c8/O2Physics/stage/bin/o2-analysis-em-pcm-qc-mc, device shutting down. Reason: Preslice not valid: table "V0PhotonsKF_001" (or join based on it) does not have column "fIndexEMEvents"
ninja: build stopped: subcommand failed.

Full log here.

[alibuild]

Error while checking build/O2Physics/o2 for c1c88e3 at 2026-02-23 16:25:

## sw/BUILD/O2Physics-latest/log
[FATAL] Unhandled o2::framework::runtime_error reached the top of main of /sw/BUILD/7c382c879c81a38aedc24c1ddf67a787890dc6c8/O2Physics/stage/bin/o2-analysis-em-pcm-qc, device shutting down. Reason: Preslice not valid: table "V0PhotonsKF_001" (or join based on it) does not have column "fIndexEMEvents"
[FATAL] Unhandled o2::framework::runtime_error reached the top of main of /sw/BUILD/7c382c879c81a38aedc24c1ddf67a787890dc6c8/O2Physics/stage/bin/o2-analysis-em-pcm-qc-mc, device shutting down. Reason: Preslice not valid: table "V0PhotonsKF_001" (or join based on it) does not have column "fIndexEMEvents"
ninja: build stopped: subcommand failed.

Full log here.

[alibuild]

Error while checking build/O2Physics/o2 for d503fba at 2026-02-23 17:14:

No log files found

Full log here.