fix: unexpected update of a btp_subaccount_service_binding

[ANUGRAHG]

Purpose

• fix #936

Does this introduce a breaking change?

[ ] Yes
[x] No

Pull Request Type

What kind of change does this Pull Request introduce?

[x] Bugfix
[ ] Feature
[ ] Refactoring (no functional changes, no api changes)
[ ] Documentation content changes
[ ] Other... Please describe:

How to Test

• Test the code via automated test

go test ./...

What to Check

Verify that the following are valid:

• Automated tests are executed successfully

Other Information

n/a

Checklist for reviewer

The following organizational tasks must be completed before merging this PR:

• [x] The PR is assigned to the Terraform project and a status is set (typically "in review").
• [x] The PR has the matching labels assigned to it.
• [x] The PR has a milestone assigned to it.
• [x] If the PR closes an issue, the issue is referenced.
• [x] Possible follow-up items are created and linked.