[release-1.3] Bump go to 1.25.8

[shuan1026]

Ref: etcd-io/etcd#21364
Ref: etcd-io/etcd#21458

From https://go.dev/doc/devel/release#go1.25.0

go1.25.7 (released 2026-02-04) includes security fixes to the go command and the crypto/tls package, as well as bug fixes to the compiler and the crypto/x509 package.
go1.25.8 (released 2026-03-05) includes security fixes to the html/template, net/url, and os packages, as well as bug fixes to the go command, the compiler, and the os package. See the Go 1.25.8 milestone on our issue tracker for details.

[ahrtr]

/ok-to-test

[ivanvc]

Same for this one, it needs a #954 backport. That's what is making the workflows fail.

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[ahrtr]

pls refer to https://github.com/etcd-io/etcd/blob/0f5cee16488816ad9e9ecb7cbdfd2aa74b163aeb/scripts/test_lib.sh#L515-L532

[fuweid]

@shuan1026 are you still working on this? 1.25.9 is out. if you don't have time, please let us know. thanks