Bump traefik version to v3.6.12

[github-actions]

Update traefik version

Bump to latest traefik version in Makefile

1 file(s) updated with "TAG := v3.6.12$$(BUILD_META)": * Makefile

v3.6.12

**CVE fixed:**
- [CVE-2026-33433](https://nvd.nist.gov/vuln/detail/CVE-2026-33433) (Advisory [GHSA-qr99-7898-vr7c](https://github.com/traefik/traefik/security/advisories/GHSA-qr99-7898-vr7c))
- [CVE-2026-33186](https://nvd.nist.gov/vuln/detail/CVE-2026-33186) (Advisory [GHSA-46wh-3698-f2cx](https://github.com/traefik/traefik/security/advisories/GHSA-46wh-3698-f2cx))

**Bug fixes:**
- **[k8s/ingress-nginx]** Fix auth-response-headers whitespace trimming in ingress-nginx provider ([#12856](https://github.com/traefik/traefik/pull/12856) @mmatur)
- **[acme]** Bump github.com/go-acme/lego/v4 to v4.33.0 ([#12840](https://github.com/traefik/traefik/pull/12840) @ldez)
- **[server]** Fix comment and unnecessary allocation in withRoutingPath ([#12880](https://github.com/traefik/traefik/pull/12880) @boinger)
- **[server, tcp]** Fix postgres STARTTLS with TLS termination ([#12847](https://github.com/traefik/traefik/pull/12847) @mmatur)
- **[api]** Fix allow colons and tildes in api.basePath validation ([#12857](https://github.com/traefik/traefik/pull/12857) @mmatur)
- **[grpc]** Bump google.golang.org/grpc to v1.79.3 ([#12845](https://github.com/traefik/traefik/pull/12845) @mmatur)
- **[middleware, authentication]** Prevent duplicate user headers in basic and digest auth middleware ([#12851](https://github.com/traefik/traefik/pull/12851) @juliens)
- **[middleware]** Fix StripPrefix and StripPrefixRegex to slice the prefix using encoded prefix length ([#12863](https://github.com/traefik/traefik/pull/12863) @gndz07)

**Documentation:**
- **[acme]** Clarify CNAME explanation in ACME Documentation ([#12818](https://github.com/traefik/traefik/pull/12818) @sheddy-traefik)
- **[k8s/ingress-nginx]** Add ingress-nginx migration banner on documentation pages ([#12872](https://github.com/traefik/traefik/pull/12872) @gndz07)
- **[k8s/ingress-nginx]** Clarify that NGINX Ingress watchNamespace watches only one namespace ([#12873](https://github.com/traefik/traefik/pull/12873) @parkerfath)
- **[k8s/ingress]** Improve Kubernetes Ingress Routing Documentation ([#12876](https://github.com/traefik/traefik/pull/12876) @sheddy-traefik)

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