build(deps): bump go.sia.tech/core

Bumps [go.sia.tech/core](https://github.com/SiaFoundation/core) from 0.20.1-0.20260505133717-19aaca8844e7 to 0.21.0.
- [Release notes](https://github.com/SiaFoundation/core/releases)
- [Changelog](https://github.com/SiaFoundation/core/blob/master/CHANGELOG.md)
- [Commits](https://github.com/SiaFoundation/core/commits/v0.21.0)

---
updated-dependencies:
- dependency-name: go.sia.tech/core
  dependency-version: 0.21.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

go.mod

@@ -6,7 +6,7 @@ require (
 	github.com/quic-go/quic-go v0.59.1
 	github.com/quic-go/webtransport-go v0.10.1-0.20260312060737-05fe5253a73c
 	go.etcd.io/bbolt v1.4.3
-	go.sia.tech/core v0.20.1-0.20260505133717-19aaca8844e7
+	go.sia.tech/core v0.21.0
 	go.sia.tech/mux v1.5.0
 	go.uber.org/zap v1.28.0
 	golang.org/x/crypto v0.51.0

go.sum

@@ -14,8 +14,8 @@ github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu
 github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
 go.etcd.io/bbolt v1.4.3 h1:dEadXpI6G79deX5prL3QRNP6JB8UxVkqo4UPnHaNXJo=
 go.etcd.io/bbolt v1.4.3/go.mod h1:tKQlpPaYCVFctUIgFKFnAlvbmB3tpy1vkTnDWohtc0E=
-go.sia.tech/core v0.20.1-0.20260505133717-19aaca8844e7 h1:h1GK0H42xEa80s+ac2xO7dTjCm9NIgNa+H+fL+7zabI=
-go.sia.tech/core v0.20.1-0.20260505133717-19aaca8844e7/go.mod h1:nZsd0YjU6slPLkpz0rxLcMJJQTKyp0hxjNIKReF7wBQ=
+go.sia.tech/core v0.21.0 h1:BtZPT/UGPj5YjDmIA31fmZIm+fmqw/X4yshskr3cOwQ=
+go.sia.tech/core v0.21.0/go.mod h1:b39iLfen0vRV3dkq1eSeBHDcaLFf89YPh2/TyBDY31Y=
 go.sia.tech/mux v1.5.0 h1:6bQeO5y4AQPcf+UYHjhxpaNX+2V2wI5LIl0BbAg2YDA=
 go.sia.tech/mux v1.5.0/go.mod h1:1/SlgVsLOUsca5tXxAEEwl+Ohm4B8te2YdRhpRGaUZw=
 go.uber.org/goleak v1.3.0 h1:2K3zAYmnTNqV73imy9J1T3WC+gmCePx2hEGkimedGto=