chore: update go version to 1.26.6 (#6835)
Go 1.26.5 carries eight HIGH severity stdlib advisories that trivy flags on every image
build, so publish-artifacts currently fails on main and on every open PR regardless of
content.
Fixed in 1.26.6: CVE-2026-33818 (encoding/asn1 DoS), CVE-2026-39821 (x/net/idna privilege
escalation), CVE-2026-46600 (x/net/dns/dnsmessage DoS), CVE-2026-56853 (net/http
unencrypted HTTP/2), CVE-2026-56858 (html/template XSS), CVE-2026-56859 (encoding/xml
DoS), CVE-2026-56860 (net/url DoS), CVE-2026-56862 (crypto/tls DoS).
Bumps the go directive in the root module and all 62 submodules, plus the three golang
base image pins. Those pins carry both a tag and a digest and docker resolves by digest,
so both are updated.
The two hack/tools modules stay on 1.26.4: they are build-time only, excluded from the
workspace, and not part of the scanned image.
Signed-off-by: Alexander Chernov <alexander@chernov.it>