Bump golang.org/x/mod from 0.20.0 to 0.21.0

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

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

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

go.mod

@@ -1,6 +1,7 @@
 module github.com/prometheus/alertmanager
 
 go 1.22
+toolchain go1.22.5
 
 require (
 	github.com/KimMachineGun/automemlimit v0.6.1
@@ -44,7 +45,7 @@ require (
 	github.com/xlab/treeprint v1.2.0
 	go.uber.org/atomic v1.11.0
 	go.uber.org/automaxprocs v1.6.0
-	golang.org/x/mod v0.20.0
+	golang.org/x/mod v0.21.0
 	golang.org/x/net v0.30.0
 	golang.org/x/text v0.19.0
 	golang.org/x/tools v0.24.0

go.sum

@@ -600,8 +600,8 @@ golang.org/x/mod v0.3.0/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
 golang.org/x/mod v0.4.0/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
 golang.org/x/mod v0.4.1/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
 golang.org/x/mod v0.4.2/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
-golang.org/x/mod v0.20.0 h1:utOm6MM3R3dnawAiJgn0y+xvuYRsm1RKM/4giyfDgV0=
-golang.org/x/mod v0.20.0/go.mod h1:hTbmBsO62+eylJbnUtE2MGJUyE7QWk4xUqPFrRgJ+7c=
+golang.org/x/mod v0.21.0 h1:vvrHzRwRfVKSiLrG+d4FMl/Qi4ukBCE6kZlTUkDYRT0=
+golang.org/x/mod v0.21.0/go.mod h1:6SkKJ3Xj0I0BrPOZoBy3bdMptDDU9oJrpohJ3eWZ1fY=
 golang.org/x/net v0.0.0-20180724234803-3673e40ba225/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20180826012351-8a410e7b638d/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20181114220301-adae6a3d119a/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=