build(deps): bump golang.org/x/mod from 0.20.0 to 0.21.0 in /multimod

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]>

multimod/go.mod

@@ -1,6 +1,7 @@
 module go.opentelemetry.io/build-tools/multimod
 
 go 1.22
+toolchain go1.22.5
 
 require (
 	github.com/go-git/go-git/v5 v5.12.0
@@ -9,7 +10,7 @@ require (
 	github.com/stretchr/testify v1.9.0
 	go.opentelemetry.io/build-tools v0.14.0
 	go.uber.org/multierr v1.11.0
-	golang.org/x/mod v0.20.0
+	golang.org/x/mod v0.21.0
 )
 
 require (

multimod/go.sum

@@ -125,8 +125,8 @@ golang.org/x/exp v0.0.0-20230905200255-921286631fa9 h1:GoHiUyI/Tp2nVkLI2mCxVkOjs
 golang.org/x/exp v0.0.0-20230905200255-921286631fa9/go.mod h1:S2oDrQGGwySpoQPVqRShND87VCbxmc6bL1Yd2oYrm6k=
 golang.org/x/mod v0.6.0-dev.0.20220419223038-86c51ed26bb4/go.mod h1:jJ57K6gSWd91VN4djpZkiMVwK6gcyfeH4XE8wZrZaV4=
 golang.org/x/mod v0.8.0/go.mod h1:iBbtSCu2XBx23ZKBPSOrRkjjQPZFPuis4dIYUhu/chs=
-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 v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
 golang.org/x/net v0.0.0-20210226172049-e18ecbb05110/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
 golang.org/x/net v0.0.0-20211112202133-69e39bad7dc2/go.mod h1:9nx3DQGgdP8bBQD5qxJ1jj9UTztislL4KSBs9R2vV5Y=