refactor(schematics): replace deprecated TestBed.get method

[salemdar]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ngrx/platform/blob/master/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)
[x] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

Data schematics are creating specs with deprecated TestBed.get method.

What is the new behavior?

Data schematics are creating specs with TestBed.inject method.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

[ngrxbot]

Preview docs changes for 0c4aba3 at https://previews.ngrx.io/pr2932-0c4aba3b/

[brandonroberts]

Thanks @salemdar!