PyModules: Add missing entrypoints dependency

@smh noticed that flake8 doesn't work in our installed python3 nightlies. It works fine during the build, so it's the usual problem of missing RPM dependencies. I suppose entrypoints in our regular builds got installed at some point by another package. So this missing dependency only showed up once we installed the LCG build from scratch in our python3 nightlies.

AE Build FAILURE
Build logfiles are available at Jenkins [AE-MERGE-REQUEST-CC7 #112]

Looks like our CI doesn't handle patching very well:

16:20:32 Reversed (or previously applied) patch detected!  Assume -R? [n] 
16:20:32 Apply anyway? [n] 
16:20:32 Skipping patch.
16:20:32 1 out of 1 hunk ignored -- saving rejects to file plugins/SISCone/SISConeBasePlugin.cc.rej
16:20:32 make[2]: *** [src/FastJet-stamp/FastJet-patch] Error 1
16:20:32 make[1]: *** [External/FastJet/CMakeFiles/FastJet.dir/all] Error 2

I assume this is interference with !569 (merged) ?

mentioned in merge request !569 (merged)

Jenkins please retry a build

AE Build SUCCESS
Build logfiles are available at Jenkins [AE-MERGE-REQUEST-CC7 #115]

merged

mentioned in commit 6db55b69