Bump golang.org/x/sys from 0.20.0 to 0.21.0 in /test/agent

Bumps [golang.org/x/sys](https://github.com/golang/sys) from 0.20.0 to 0.21.0.
- [Commits](golang/sys@v0.20.0...v0.21.0)

---
updated-dependencies:
- dependency-name: golang.org/x/sys
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

test/agent/go.mod

@@ -5,7 +5,7 @@ go 1.22.3
 require (
 	github.com/coreos/go-iptables v0.7.0
 	github.com/vishvananda/netlink v1.1.0
-	golang.org/x/sys v0.20.0
+	golang.org/x/sys v0.21.0
 )
 
 require github.com/vishvananda/netns v0.0.0-20191106174202-0a2b9b5464df // indirect

test/agent/go.sum

@@ -5,5 +5,5 @@ github.com/vishvananda/netlink v1.1.0/go.mod h1:cTgwzPIzzgDAYoQrMm0EdrjRUBkTqKYp
 github.com/vishvananda/netns v0.0.0-20191106174202-0a2b9b5464df h1:OviZH7qLw/7ZovXvuNyL3XQl8UFofeikI1NW1Gypu7k=
 github.com/vishvananda/netns v0.0.0-20191106174202-0a2b9b5464df/go.mod h1:JP3t17pCcGlemwknint6hfoeCVQrEMVwxRLRjXpq+BU=
 golang.org/x/sys v0.0.0-20190606203320-7fc4e5ec1444/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/sys v0.20.0 h1:Od9JTbYCk261bKm4M/mw7AklTlFYIa0bIp9BgSm1S8Y=
-golang.org/x/sys v0.20.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
+golang.org/x/sys v0.21.0 h1:rF+pYz3DAGSQAxAu1CbC7catZg4ebC4UIeIhKxBZvws=
+golang.org/x/sys v0.21.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=