.angular cache folder not ignored after ng update to v13

[fmalcher]

🐞 Bug report

Command (mark with an x)

• update

Is this a regression?

Yes, the previous version in which this bug was not present was: 12.2.10

Description

Newly created projects with 13.0.0-rc.0 have the .angular cache folder added to .gitignore.
When updating from a v12.2.10 project, the entry is not added, hence the folder is not ignored.

🔬 Minimal Reproduction

# create new project with globally installed CLI 13.0.0-rc.0
ng new foofoo --routing=false --style=css

=> ✅ has /.angular/cache in .gitignore

# create new project with globally installed CLI 12.2.10
ng new foofoo --routing=false --style=css
cd foofoo

# update to 13.0.0-rc.0
ng update @angular/cli --next

=> ❌ does NOT have /.angular cache folder ignored!

🌍 Your Environment

Angular CLI: 13.0.0-rc.0
Node: 14.17.6
Package Manager: npm 6.14.15
OS: darwin x64

Angular: 13.0.0-rc.0
... animations, cli, common, compiler, compiler-cli, core, forms
... platform-browser, platform-browser-dynamic, router

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