[Dev] Update apache/arrow-site GitHub Actions deploy.yml website deployment workflow to support being triggered when pushing to main

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As part of the transition away from using the name master for the default Git branch, we need to update the GitHub Actions website deployment workflow trigger.

Since there does not appear to be any way to dynamically compute the default Git branch name in a GitHub Actions push trigger condition, a temporary workaround would be to add support for pushing to either master or {}main{}.

Once Apache Infra switches the default Git branch for apache/arrow-site to {}main{}, we can completely remove support for triggering the GitHub Actions website deployment workflow on pushes to master from {}.github/workflows/deploy.yml{}. This follow up work is tracked by ARROW-15988.

The main file that will need updating is {}.github/workflows/deploy.yml{}.

Reporter: Neal Richardson / @nealrichardson
Assignee: Kevin Gurney / @kevingurney

_{Note: This issue was originally created as ARROW-15694. Please see the migration documentation for further details.}

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Kouhei Sutou / @kou:
Issue resolved by pull request 202
apache/arrow-site#202

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Kevin Gurney / @kevingurney:
Merged via apache/arrow-site#202