PWGLF: Update the number of injected particle for PbPb

[BongHwi]

So far, we intend to inject only one particle per event.

But in PbPb collision, we could increase this to save the computing resources.

We updated the number of injected particles in the PbPb injector case.

[github-actions]

REQUEST FOR PRODUCTION RELEASES:
To request your PR to be included in production software, please add the corresponding labels called "async-" to your PR. Add the labels directly (if you have the permissions) or add a comment of the form (note that labels are separated by a ",")

+async-label <label1>, <label2>, !<label3> ...

This will add <label1> and <label2> and removes <label3>.

The following labels are available
async-2022-pp-apass4
async-2023-pbpb-apass3
async-2023-pbpb-apass4
async-2022-pp-apass6-2023-PbPb-apass2
async-2022-pp-apass4-accepted
async-2022-pp-apass6-2023-PbPb-apass2-accepted
async-2023-pbpb-apass3-accepted
async-2023-pbpb-apass4-accepted

[BongHwi]

+async-label async-2022-pp-apass6-2023-PbPb-apass2 async-2023-pbpb-apass3 async-2023-pbpb-apass4

[github-actions]

Hi @BongHwi, the following label names could not be recognised: async-2022-pp-apass6-2023-PbPb-apass2 async-2023-pbpb-apass3 async-2023-pbpb-apass4

[BongHwi]

+async-label async-2022-pp-apass6-2023-PbPb-apass2,async-2023-pbpb-apass3,async-2023-pbpb-apass4