fix auto-print detection on R 3.4/3.5 where sys.calls() returns a promise

[skitsy24]

Closes #7099.

On R 3.4 and 3.5, the top-level call captured via sys.calls() during auto-print is not a direct reference to base::print, but a promise object that evaluates to it. As a result, the existing check:

identical(SYS[[1L]][[1L]], print)

fails, and print.data.table() incorrectly treats auto-print as an explicit print() call. This leads to unintended output in cases where printing should be suppressed (e.g., after := assignments).

Thanks to @aitap for identifying the root cause.

My fix adds a check on whether print() is wrapped in a "promise" to differentiate between the older R versions. If it is a promise, the promise is evaluated, and then checked against print.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.04%. Comparing base (3a45206) to head (194ef2b).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7727   +/-   ##
=======================================
  Coverage   99.04%   99.04%           
=======================================
  Files          87       87           
  Lines       17123    17043   -80     
=======================================
- Hits        16959    16880   -79     
+ Misses        164      163    -1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[aitap]

This disappeared in R-3.6.0, right? Let's wrap this branch in # nocov start ... # nocov end and add a # TODO(R>=3.6) comment to remove it once we raise the minimal supported R version.