GEODE-10586: Update Homebrew clone to use main branch

[JinwooHwang]

Changes

Updated dev-tools/release/prepare_rc.sh to clone the Homebrew/homebrew-core repository using the main branch instead of master.

Homebrew renamed their default branch from master to main, so the release preparation script needs to be updated accordingly.

Modified Files

• dev-tools/release/prepare_rc.sh

Details

-git clone --single-branch --branch master git@github.com:Homebrew/homebrew-core.git
+git clone --single-branch --branch main git@github.com:Homebrew/homebrew-core.git

For all changes, please confirm:

• Is there a JIRA ticket associated with this PR? Is it referenced in the commit message?
• Has your PR been rebased against the latest commit within the target branch (typically develop)?
• Is your initial contribution a single, squashed commit?
• Does gradlew build run cleanly?
• Have you written or updated unit tests to verify your changes?
• If adding new dependencies to the code, are these dependencies licensed in a way that is compatible for inclusion under ASF 2.0?