Bugfix vgac reader

[ninahakansson]

Fix a bug I intruded when writing unit test for the time var in the vgac reader. The time_proj0 is a scalar in the files, and now also in the unittest case.

• [x] Tests added

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 95.94%. Comparing base (7e336ee) to head (85d9117). Report is 11 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2754 +/- ## ======================================= Coverage 95.93% 95.94% ======================================= Files 375 375 Lines 53223 53293 +70 ======================================= + Hits 51058 51130 +72 + Misses 2165 2163 -2 ``` | [Flag](https://app.codecov.io/gh/pytroll/satpy/pull/2754/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pytroll) | Coverage Δ | | |---|---|---| | [behaviourtests](https://app.codecov.io/gh/pytroll/satpy/pull/2754/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pytroll) | `4.12% <0.00%> (-0.01%)` | :arrow_down: | | [unittests](https://app.codecov.io/gh/pytroll/satpy/pull/2754/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pytroll) | `96.03% <100.00%> (+<0.01%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pytroll#carryforward-flags-in-the-pull-request-comment) to find out more.

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[coveralls]

Pull Request Test Coverage Report for Build 8204057910

Details

• 2 of 2 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 96.02%

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Totals
Change from base Build 8200761354:	0.0%
Covered Lines:	51002
Relevant Lines:	53116

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💛 - Coveralls