Update Go to 1.26.1 and golangci-lint to v2.11.4

What does this MR do?

• Updates Go to 1.26.1.
• Updates golangci-lint to v2.11.4 (required to support linting Go 1.26 projects).
• Resolves issues flagged by go vet (which caused go test build failures) in the new Go version.
• Resolves issues flagged by staticcheck in the new golangci-lint version.

Why was this MR needed?

To resolve vulnerabilities in Go.

What's the best way to test this MR?

Check that CI passes.

What are the relevant issue numbers?

Closes #39341 (closed)