build: update to Angular 20-rc

[timdeschryver]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ngrx/platform/blob/main/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[x] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

Closes #

What is the new behavior?

• the TestBed.flushEffects() was removed - use the TestBed.tick() instead. (https://github.com/angular/angular/blob/main/CHANGELOG.md#2000-next9-2025-04-30)
• refactored a leftover TestBed.get to TestBed.inject
• updated snapshots

Does this PR introduce a breaking change?

[x] Yes
[ ] No

Other information

While running pnpm i I noticed some old packages that can be updated/removed.
This can be done after this PR is merged.

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