Use diff suppress func for binary authorization attestor

[modular-magician]

GoogleCloudPlatform/magic-modules#4575 introduced a diff suppress func for algorithm signature but it was not actually ever added to the relevant field. This PR fixes that oversight.

Resolved #8511

Unfortunately this is difficult to test, because the tests require a bootstrapped KMS key, which does not currently allow specifying an algorithm - and changing that test code is not trivial.

If this PR is for Terraform, I acknowledge that I have:

• Searched through the issue tracker for an open issue that this either resolves or contributes to, commented on it to claim it, and written "fixes {url}" or "part of {url}" in this PR description. If there were no relevant open issues, I opened one and commented that I would like to work on it (not necessary for very small changes).
• Generated Terraform, and ran make test and make lint to ensure it passes unit and linter tests.
• Ensured that all new fields I added that can be set by a user appear in at least one example (for generated resources) or third_party test (for handwritten resources or update tests).
• Ran relevant acceptance tests (If the acceptance tests do not yet pass or you are unable to run them, please let your reviewer know).
• Read the Release Notes Guide before writing my release note below.

Release Note Template for Downstream PRs (will be copied)

binaryauthorization: fixed permadiff in `google_binary_authorization_attestor`

Derived from GoogleCloudPlatform/magic-modules#5967

[github-actions]

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