Bump Go to v1.26.4 and update dependencies

[hjiawei]

Description

Release Note

Bump Go to v1.26.4 and update Kubernetes to v1.36.2.

For PR author

• Tests for change.
• If changing pkg/apis/, run make gen-files
• If changing versions, run make gen-versions

For PR reviewers

A note for code reviewers - all pull requests must have the following:

• Milestone set according to targeted release.
• Appropriate labels:
  • kind/bug if this is a bugfix.
  • kind/enhancement if this is a a new feature.
  • enterprise if this PR applies to Calico Enterprise only.

[Copilot]

Pull request overview

Updates the operator’s build/toolchain configuration to Go 1.26.4 and refreshes a broad set of Go module dependencies (including Helm, Kubernetes, AWS SDK, and testing libraries) to newer versions.

Changes:

• Bump build toolchain inputs (Go build image tag and Helm CLI version) in the Makefile.
• Update Go module versions across the root module and the api/ submodule (go directive + dependency bumps).
• Regenerate go.sum files to reflect the updated module graph.

Reviewed changes

Copilot reviewed 3 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
Makefile	Updates Helm version and build image/version inputs for Go/Kubernetes base.
go.mod	Bumps Go version and updates direct/indirect dependency versions (notably k8s, aws-sdk-go-v2, helm).
go.sum	Updates dependency checksums for the root module after module upgrades.
api/go.mod	Bumps Go version and updates dependencies for the API submodule.
api/go.sum	Updates dependency checksums for the API submodule after module upgrades.

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