all: upgrade go directive to at least 1.26.0 [generated]

By now Go 1.27.0 has been released, and Go 1.25 is no longer supported
per the Go Release Policy (see https://go.dev/doc/devel/release#policy).

See https://go.dev/doc/godebug#go-126 for GODEBUG setting changes
relevant to Go 1.26.

For golang/go#69095.

[git-generate]
(cd . && go get go@1.26.0 && go mod tidy)

Change-Id: I4825f5f94875a8e76dd3fad60e66158f9d8ad899
Reviewed-on: https://go-review.googlesource.com/c/sys/+/817820
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>