Fix pacman repo build

[acolwell]

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• I've followed the contributing guidelines to the best of my understanding
• I've read and understood the contributing guidelines
• I've formatted my code according to Natron's code style
• I've searched the pull requests tracker to ensure that this PR is not a duplicate

PR Description

What type of PR is this? (Check one of the boxes below)

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Improvement (non-breaking change which does not add functionality nor fixes a bug but improves Natron in some way)
• Breaking change (fix or feature that would cause existing functionality to change)
• My change requires a change to the documentation
  • I have updated the documentation accordingly

What does this pull request do?

This fixes pacman repo build failures.

• The OpenImageIO source tar ball changed the directory name it stores the source files in, which in turn caused the sha256sum to change. The directory name and tarball sha256sum were updated.
• Some index hashes in an ffmpeg patch we were fetching from github now have extra digits. This caused the sha256sum to change, which caused the build to fail. The sha256sum was updated for the patch file.

Have you tested your changes (if applicable)? If so, how?

Yes. I've verified the pacman repo successfully builds with these changes .(https://github.com/acolwell/Natron/actions/runs/6398435536)

[devernay]

LGTM