Update module golang.org/x/net to v0.51.0 [SECURITY] (v11.0/forgejo) (#11831)

This PR contains the following updates:

| Package | Change | [Age](https://docs.renovatebot.com/merge-confidence/) | [Confidence](https://docs.renovatebot.com/merge-confidence/) |
|---|---|---|---|
| [golang.org/x/net](https://pkg.go.dev/golang.org/x/net) | [`v0.50.0` → `v0.51.0`](https://cs.opensource.google/go/x/net/+/refs/tags/v0.50.0...refs/tags/v0.51.0) | ![age](https://developer.mend.io/api/mc/badges/age/go/golang.org%2fx%2fnet/v0.51.0?slim=true) | ![confidence](https://developer.mend.io/api/mc/badges/confidence/go/golang.org%2fx%2fnet/v0.50.0/v0.51.0?slim=true) |

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> ⚠️ **Warning**
>
> Some dependencies could not be looked up. Check the [Dependency Dashboard](issues/2779) for more information.

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### Sending certain HTTP/2 frames can cause a server to panic in golang.org/x/net
[CVE-2026-27141](https://nvd.nist.gov/vuln/detail/CVE-2026-27141) / [GO-2026-4559](https://pkg.go.dev/vuln/GO-2026-4559)

<details>
<summary>More information</summary>

#### Details
Due to missing nil check, sending 0x0a-0x0f HTTP/2 frames will cause a running server to panic

#### Severity
Unknown

#### References
- [https://nvd.nist.gov/vuln/detail/CVE-2026-27141](https://nvd.nist.gov/vuln/detail/CVE-2026-27141)
- [https://go.dev/cl/746180](https://go.dev/cl/746180)
- [https://go.dev/issue/77652](https://go.dev/issue/77652)

This data is provided by [OSV](https://osv.dev/vulnerability/GO-2026-4559) and the [Go Vulnerability Database](https://github.com/golang/vulndb) ([CC-BY 4.0](https://github.com/golang/vulndb#license)).
</details>

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Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/11831
Reviewed-by: Mathieu Fenniak <mfenniak@noreply.codeberg.org>
Co-authored-by: Renovate Bot <bot@kriese.eu>
Co-committed-by: Renovate Bot <bot@kriese.eu>

go.mod

@@ -102,7 +102,7 @@ require (
 	go.uber.org/mock v0.5.0
 	golang.org/x/crypto v0.48.0
 	golang.org/x/image v0.38.0
-	golang.org/x/net v0.50.0
+	golang.org/x/net v0.51.0
 	golang.org/x/oauth2 v0.28.0
 	golang.org/x/sync v0.20.0
 	golang.org/x/sys v0.41.0

go.sum

@@ -731,8 +731,8 @@ golang.org/x/net v0.15.0/go.mod h1:idbUs1IY1+zTqbi8yxTbhexhEEk5ur9LInksu6HrEpk=
 golang.org/x/net v0.21.0/go.mod h1:bIjVDfnllIU7BJ2DNgfnXvpSvtn8VRwhlsaeUTyUS44=
 golang.org/x/net v0.25.0/go.mod h1:JkAGAh7GEvH74S6FOH42FLoXpXbE/aqXSrIQjXgsiwM=
 golang.org/x/net v0.33.0/go.mod h1:HXLR5J+9DxmrqMwG9qjGCxZ+zKXxBru04zlTvWlWuN4=
-golang.org/x/net v0.50.0 h1:ucWh9eiCGyDR3vtzso0WMQinm2Dnt8cFMuQa9K33J60=
-golang.org/x/net v0.50.0/go.mod h1:UgoSli3F/pBgdJBHCTc+tp3gmrU4XswgGRgtnwWTfyM=
+golang.org/x/net v0.51.0 h1:94R/GTO7mt3/4wIKpcR5gkGmRLOuE/2hNGeWq/GBIFo=
+golang.org/x/net v0.51.0/go.mod h1:aamm+2QF5ogm02fjy5Bb7CQ0WMt1/WVM7FtyaTLlA9Y=
 golang.org/x/oauth2 v0.0.0-20180821212333-d2e6202438be/go.mod h1:N/0e6XlmueqKjAGxoOufVs8QHGRruUQn6yWY3a++T0U=
 golang.org/x/oauth2 v0.0.0-20190226205417-e64efc72b421/go.mod h1:gOpvHmFTYa4IltrdGE7lF6nIHvwfUNPOp7c8zoXwtLw=
 golang.org/x/oauth2 v0.0.0-20190604053449-0f29369cfe45/go.mod h1:gOpvHmFTYa4IltrdGE7lF6nIHvwfUNPOp7c8zoXwtLw=