Fix webhook signature header

[valentinbourgoin]

Hi guys,

Following Airtable documentation here, the X-Airtable-Content-MAC header contains a hmac-sha256= prefix. In the WebhookNotification.from_request() method, a wrong prefix hmac-sha256- is added to the expected hashed value.

Thanks for your work 🙏

[codecov[bot]]

Codecov Report

Merging #312 (488d257) into main (308c269) will not change coverage. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #312   +/-   ##
=======================================
  Coverage   96.11%   96.11%           
=======================================
  Files          21       21           
  Lines        1157     1157           
=======================================
  Hits         1112     1112           
  Misses         45       45           

Files	Coverage Δ
pyairtable/models/webhook.py	100.00% <100.00%> (ø)

[mesozoic]

Oops, that is just a straight up typo. Good catch, and thanks for contributing!

This repo requires all commits to be signed, which is pretty easy to do with an SSH key. Do you mind setting that up, amending your commit, and force-pushing to update the PR branch? I could rebase the branch for you, but then GitHub won't give you any credit for the fix. :)

[mesozoic]

@valentinbourgoin If you've got time to rebase your branch with signed commits enabled, I will merge this as-is so GitHub will give you credit 😁. If I don't hear back in a few days, I'll copy the branch and merge it myself.

[valentinbourgoin]

Hey @mesozoic, My commit is verified now :) Thanks !!