Upgrade Go to 1.26.1

[lukeheath]

Goal

User story
As an individual contributor to Fleet,
I want to know that Fleet is running the latest major and minor version of Go
so that I can benefit from bug fixes and use new features.

Changes

Engineering

• Test plan is finalized

ℹ️  Please read this issue carefully and understand it. Pay special attention to UI wireframes, especially "dev notes".

Risk assessment

• Risk level: Low

Test plan

Make sure to go through the list and consider all events that might be related to this story, so we catch edge cases earlier.

• Ensure all automated tests are passing.

Testing notes

[lukeheath]

@getvictor Per the release candidate release process, I'm filing this story to upgrade to the latest version of Go. The Eng Ops working group spun down today, so I'm assigning to S&C. I think it makes sense for Go upgrades to default to S&C moving forward to have a clear product group own the upgrades.