[Chapel Merge] Fix a malformed date in the script that runs chapcs playground

Branch: refs/heads/main
Revision: 2424d26f885471994654f730e8d0cb9e81a5a3df
Author: dlongnecke-cray
Link: Fix a malformed date in the script that runs chapcs playground by dlongnecke-cray · Pull Request #28786 · chapel-lang/chapel · GitHub
Log Message:
Fix a malformed date in the script that runs chapcs playground (#28786)

We weren't actively using this playground, but this config has been
going yellow for a week because I put a malformed date into the script.
Fix that.

Compare: Comparing 7e67ea5405b1be99f32a6a23a525cf32c7f480f4...d3938246f1254450d10500c305a1dfbf0005a5f7 · chapel-lang/chapel · GitHub

Diff:
M util/cron/test-perf.chapcs.playground.bash
https://github.com/chapel-lang/chapel/pull/28786.diff