add comment to explain gufe pin in env yamls

[atravitz]

Thanks @jthorton for flagging that this is confusing.

Checklist

• Added a news entry

Developers certificate of origin

• I certify that this contribution is covered by the MIT License here and the Developer Certificate of Origin at https://developercertificate.org/.

[github-actions]

No API break detected ✅

[jthorton]

LGTM!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.19%. Comparing base (48a9500) to head (ebb7ead).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1553      +/-   ##
==========================================
- Coverage   95.25%   93.19%   -2.06%     
==========================================
  Files         172      172              
  Lines       14467    14467              
==========================================
- Hits        13780    13483     -297     
- Misses        687      984     +297     

Flag	Coverage Δ
fast-tests	93.19% <ø> (?)
slow-tests	?

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