use `group_by()` instead

[emagar]

In ubuntu 22.04 with a fresh R 4.3.2 installation, I got this warning after invoking slide():

Lagging cycle by 1 time units.

Warning message:
group_by_() was deprecated in dplyr 0.7.0.
ℹ Please use group_by() instead.
ℹ See vignette('programming') for more help
ℹ The deprecated feature was likely used in the DataCombine package.
Please report the issue at https://github.com/christophergandrud/DataCombine/issues.
This warning is displayed once every 8 hours.
Call lifecycle::last_lifecycle_warnings() to see where this warning was generated.

lifecycle::last_lifecycle_warnings()
[[1]]
<warning/lifecycle_warning_deprecated>
Warning:
group_by_() was deprecated in dplyr 0.7.0.
ℹ Please use group_by() instead.
ℹ See vignette('programming') for more help
ℹ The deprecated feature was likely used in the DataCombine package.
Please report the issue at https://github.com/christophergandrud/DataCombine/issues.

---

Backtrace:
▆

1. └─DataCombine::slide(...)
2. └─dplyr::group_by_(data, .dots = GroupVar)

3. └─dplyr:::lazy_deprec("group_by")