chore: export /lib/mutation/mutation at index.ts

[jg4n]

• Affected version:
  @angular-architects/ngrx-toolkit@20.4.1

• Problem:

error TS4023: Exported variable 'MyOwnStoreInLib' has or is using name 'Mutation' from external module 

"C:/..../node_modules/@angular-architects/ngrx-toolkit/index" but cannot be named.

• Fix:
  Apply export for ./lib/mutation/mutation (.ts) file.

[rainerhahnekamp]

Thanks @jg4n