fix: close issue_write state updates with REST

[he-yufeng]

Summary

• send normal issue_write close updates through the REST PATCH request when the close reason is not duplicate
• keep the GraphQL close path for duplicate closes, where GitHub also needs the duplicate issue id
• add a regression test for closing an issue with labels and state_reason: completed in one call

Fixes #2636.

To verify

• go test ./pkg/github -run Test_UpdateIssue -count=1
• go test ./pkg/github -count=1
• go test ./...
• git diff --check

[he-yufeng]

Rebased this branch onto current main and reran the repository test suite.

Validation:

go test ./...
git diff --check origin/main..HEAD

Current head: 03febb4.