Set the Vagrant box URL for CentOS Stream 9

[ekohl]

There's no centos/stream9 box so the URL must be set.

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -0.01 ⚠️

Comparison is base (7789a2d) 0.66% compared to head (f57cad6) 0.66%.

❗ Current head f57cad6 differs from pull request most recent head 5e0a885. Consider uploading reports for the commit 5e0a885 to get more accurate results

Additional details and impacted files

@@            Coverage Diff            @@
##           master    #301      +/-   ##
=========================================
- Coverage    0.66%   0.66%   -0.01%     
=========================================
  Files          15      15              
  Lines        1941    1945       +4     
=========================================
  Hits           13      13              
- Misses       1928    1932       +4     

Impacted Files	Coverage Δ
lib/beaker-hostgenerator/data.rb	0.00% <0.00%> (ø)

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