TestPackageRevisionLifeCycle is flaky due to asynchronous revision update

### What happened?

`TestPackageRevisionLifeCycle` is occasionally flaky.

The test updates a `Function` resource and waits for:

```go
metadata.generation == 2
```

It then immediately verifies that `status.currentRevision` has changed.

However, `metadata.generation` is updated by the API server as soon as the spec
changes, while `status.currentRevision` is updated asynchronously by the package
reconciler. There is a reconciliation window where the generation has already
been incremented but the current revision still points to the previous
`FunctionRevision`.

This occasionally causes failures such as:

```
expected current revision to change, still "function-image-config-runtime-..."
```

The issue appears to be limited to the test synchronization rather than the
runtime behavior itself.

### How can we reproduce it?

Run the package lifecycle E2E test repeatedly, for example:

```bash
./nix.sh run .#e2e -- \
-test.run '^TestPackageRevisionLifeCycle$'
```

The failure is intermittent and may require several runs before reproducing.

### Suggested fix

Instead of checking `status.currentRevision` immediately after
`metadata.generation` changes, the test should wait until the current revision
actually changes (or until the new `FunctionRevision` becomes the current and
healthy revision).

This would synchronize the test on the state it is actually validating, rather
than on an intermediate reconciliation step.

### What environment did it happen in?

Crossplane version: current `main` (observed after commit `93cc669a6`)

Kubernetes: Kind (E2E test environment)

Run the package lifecycle E2E test with `./nix.sh run .#e2e -- -test.run '^TestPackageRevisionLifeCycle$'` and locate `TestPackageRevisionLifeCycle`. Read the existing wait for `metadata.generation == 2`; synchronize next on the changed or healthy `status.currentRevision`, then repeat the test to confirm the intermittent failure is gone.

Written by the indexing model from the issue text.