fix: temporarily allow forked repos to run PR workflows

[gustavovalverde]

Motivation

The continuous deployment refactors included a workflow to cache Zcash parameters, which was triggered by a pull_request event. But when triggered from a forked repo, this event does not have the right context nor permissions to read secrets

Specifications

https://docs.github.com/en/actions/using-workflows/events-that-trigger-workflows#pull_request_target

Solution

Temporarily use pull_request_target instead of pull_request

Review

@teor2345

Follow Up Work

This is a temporal fix, which needs to be solved with #3419

[teor2345]

Thanks for getting this done so quickly!

(And thanks for linking the follow-up ticket in the PR, it's good to know what the next steps are.)

[codecov]

Codecov Report

Merging #3503 (a26afc8) into main (499ae89) will increase coverage by 0.15%.
The diff coverage is 74.66%.

❗ Current head a26afc8 differs from pull request most recent head 1e51bd7. Consider uploading reports for the commit 1e51bd7 to get more accurate results

@@            Coverage Diff             @@
##             main    #3503      +/-   ##
==========================================
+ Coverage   78.34%   78.49%   +0.15%     
==========================================
  Files         267      273       +6     
  Lines       31526    31900     +374     
==========================================
+ Hits        24698    25041     +343     
- Misses       6828     6859      +31     

[dconnolly]

We should not update a direct dependency of our Docker image to be writeable by a PR from anywhere, a local branch or a fork branch, before that change has been approved by a human and merged to #main :

zebra/docker/Dockerfile.build

Line 58 in a872f17

COPY --from=us-docker.pkg.dev/zealous-zebra/zebra/zcash-params /root/.zcash-params /root/.zcash-params