[AUR] A few fixes to the update-aur.sh script
[AUR] A few fixes to the update-aur.sh script

Summary:
 - The `updpkgsums` script is expected to replace the sums using the
  algorithm already declared in the PKGBUILD. The `update-aur.sh` script
  actually does this by declaring the sums as sha256 in the PKGBUILD file,
  but this is not enough to trigger the detection by `updpkgsums`. This
  diff fixes this by adding a dummy hash value.
 - The `cp -R "${PACKAGE}"/* "${PACKAGE}-upstream"` glob expansion will
  not copy the `.SRCINFO` file due to it starting with a dot. This diff
  fixes the copy syntax to include all files including the hidden ones.

Test Plan:
  ./update-aur.sh bitcoin-abc
Check the checksum is using sha256 as expected.
Check the `.SRCINFO` file is part of the commit.

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D7306

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