go.mod: bump Go to 1.26.4 (#95)

## Summary
- bump Go from 1.26.3 to 1.26.4
- run `go mod tidy`

## Verification
- `go get -u go@latest`
- `go mod tidy`

*Generated with the `latestgo` tool. I am only a tool. If this was a mistake, the mistake was upstream of me.*

Submitted-by: latestgo
Automated-Submission: true

Author: astrophena

go.mod

@@ -1,6 +1,6 @@
 module go.astrophena.name/cloudshell
 
-go 1.26.3
+go 1.26.4
 
 require (
 	go.astrophena.name/base v0.19.1