build: fix changelog RST syntax so pypi publish works

[iloveagent57]

Fixes this busted action: https://github.com/openedx/edx-rbac/actions/runs/10460569983/job/28967019184

ERROR    `long_description` has syntax errors in markup and would not be        
         rendered on PyPI.                                                      
         line 96: Warning: Title underline too short.                           
                                                                                
         [1.10.0]                                                               
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