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] <support@github.com>

examples/oci-image-verification/go.mod

@@ -86,7 +86,7 @@ require (
  go.uber.org/zap v1.27.0 // indirect
  golang.org/x/crypto v0.27.0 // indirect
  golang.org/x/exp v0.0.0-20240112132812-db7319d0e0e3 // indirect
- golang.org/x/mod v0.20.0 // indirect
+ golang.org/x/mod v0.21.0 // indirect
  golang.org/x/net v0.27.0 // indirect
  golang.org/x/sync v0.8.0 // indirect
  golang.org/x/sys v0.25.0 // indirect

examples/oci-image-verification/go.sum

@@ -356,8 +356,8 @@ golang.org/x/crypto v0.27.0 h1:GXm2NjJrPaiv/h1tb2UH8QfgC/hOf/+z0p6PT8o1w7A=
 golang.org/x/crypto v0.27.0/go.mod h1:1Xngt8kV6Dvbssa53Ziq6Eqn0HqbZi5Z6R0ZpwQzt70=
 golang.org/x/exp v0.0.0-20240112132812-db7319d0e0e3 h1:hNQpMuAJe5CtcUqCXaWga3FHu+kQvCqcsoVaQgSV60o=
 golang.org/x/exp v0.0.0-20240112132812-db7319d0e0e3/go.mod h1:idGWGoKP1toJGkd5/ig9ZLuPcZBC3ewk7SzmH0uou08=
-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 v0.27.0 h1:5K3Njcw06/l2y9vpGCSdcxWOYHOUk3dVNGDXN+FvAys=
 golang.org/x/net v0.27.0/go.mod h1:dDi0PyhWNoiUOrAS8uXv/vnScO4wnHQO4mj9fn/RytE=
 golang.org/x/oauth2 v0.22.0 h1:BzDx2FehcG7jJwgWLELCdmLuxk2i+x9UDpSiss2u0ZA=