web: update web section modification date in post-upgrade

Post upgrader constraint to automatically fix modification date and an upgrader bug-fix for an issue that's revealed in this new test.

/reviewed-on !1013
4 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
passed SlapOS.Eggs.UnitTest-Master.Python2

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passed SlapOS.Eggs.UnitTest-Master.Python3

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passed SlapOS.Eggs.UnitTest-luke.Python2

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passed SlapOS.Eggs.UnitTest-luke.Python3

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