fix: Correct base path for GIF stickers

[Jiralite]

Please describe the changes this PR makes and why it should be merged:
GIF stickers must be accessed via the media proxy.¹

Status and versioning classification:

• Code changes have been tested against the Discord API, or there are no code changes
• I know how to update typings and have done so, or typings don't need updating

Footnotes

1. https://discord.com/developers/docs/reference#image-formatting-cdn-endpoints ↩

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2 Ignored Deployments

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 41.07%. Comparing base (7f60a8f) to head (5f06b95).

Additional details and impacted files

@@             Coverage Diff             @@
##             main   #10330       +/-   ##
===========================================
+ Coverage   19.37%   41.07%   +21.70%     
===========================================
  Files          32       49       +17     
  Lines        6267     8944     +2677     
  Branches      115      392      +277     
===========================================
+ Hits         1214     3674     +2460     
- Misses       5053     5267      +214     
- Partials        0        3        +3     

Flag	Coverage Δ
proxy	78.52% <ø> (+59.38%)	⬆️
rest	92.68% <100.00%> (+73.54%)	⬆️
ws	51.73% <ø> (+32.59%)	⬆️

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[ckohen]

(not blocking on it, but tests would be nice)