sync-tags: run go mod tidy after updating deps in go.mod
sync-tags: run go mod tidy after updating deps in go.mod

Consider a repo (like component-base) that depends on apimachinery, api
(which depnds on apimachinery) and client-go (which depends on
apimachinery and api). In the current case, sync-tags updates the tags
in component-base's go.mod in the following way:

1. Update tag for apimachinery, run `go mod tidy`
2. Update tag for api, run `go mod tidy`
3. Update tag for client-go, run `go mod tidy`

If we remove a package from api and it's references in client-go in k/k,
step 2 fails while running `go mod tidy` because the go.mod file still
contains the old client-go version i.e. client-go still references
the removed package.

To fix this, we should update tags for all dependencies and _then_ run
`go mod tidy`. We also use this approach in util.sh while syncing code
using pseudoversions so we don't face any error there.

---

This fixes errors like:

```
k8s.io/component-base/metrics/prometheus/clientgo/leaderelection imports
    k8s.io/client-go/tools/leaderelection tested by
    k8s.io/client-go/tools/leaderelection.test imports
    k8s.io/client-go/kubernetes/fake imports
    k8s.io/api/auditregistration/v1alpha1: module k8s.io/api@latest found (v0.19.0-beta.1, replaced by k8s.io/api@v0.19.0-beta.1), but does not contain package k8s.io/api/auditregistration/v1alpha1
```

kubernetes/publishing-bot,kubernetes/publishing-bot