Wait for informer cache to be populated before starting Typha autoscaler in UT

[hjiawei]

Description

This change adds a wait for fake nodes to be populated in the shared index informer cache before start Typha autoscaler.

Speculative fix for a Typha autoscaler flake:

2026-01-06T14:40:31Z	ERROR	typha_autoscaler	Failed to autoscale typha	{"error": "not enough linux nodes to schedule typha pods on, require 1 and have 0"}
github.com/tigera/operator/pkg/controller/installation.(*typhaAutoscaler).start.func1
	/go/src/github.com/tigera/operator/pkg/controller/installation/typha_autoscaler.go:143
panic: 
	assert: mock: I don't know what to return because the method call was unexpected.
		Either do Mock.On("SetDegraded").Return(...) first, or remove the SetDegraded() call.
		This method was unexpected:
			SetDegraded(v1.TigeraStatusReason,string,<nil>,logr.Logger)
			0: "ResourceScalingError"
			1: "Failed to autoscale typha - not enough linux nodes to schedule typha pods on, require 1 and have 0"
			2: <nil>
			3: logr.Logger{sink:(*log.delegatingLogSink)(0xc0002f9c40), level:0}

Release Note

TBD

For PR author

• Tests for change.
• If changing pkg/apis/, run make gen-files
• If changing versions, run make gen-versions

For PR reviewers

A note for code reviewers - all pull requests must have the following:

• Milestone set according to targeted release.
• Appropriate labels:
  • kind/bug if this is a bugfix.
  • kind/enhancement if this is a a new feature.
  • enterprise if this PR applies to Calico Enterprise only.

[hjiawei]

The golang and k8s version update changes are moved to #4348. I will rebase this PR after it is merged into the main branch.

[caseydavenport]

Thanks @hjiawei !