has_tests has a false negative when a package has tests but does not use a testing package in its Suggests

[sfirke]

For instance data.table has has_tests = FALSE in its results. I don't immediately grasp their CI pipeline but it's complex. Since packagemetrics can find that their test_coverage = CodeCov, I propose that after compiling all info, packagemetrics should check if there's a value for test_coverage, then if so, set has_tests = TRUE. Not a clean solution but a quick one.

Example as of 2022-02-03:

> library(packagemetrics)
> library(dplyr)
> 
> dplyr_and_dt <- package_list_metrics(c("dplyr", "data.table"))
> glimpse(dplyr_and_dt)
Rows: 2
Columns: 17
$ package            <chr> "dplyr", "data.table"
...
$ has_tests          <lgl> TRUE, FALSE
...
$ ci                 <chr> "NONE", "Appveyor"
$ test_coverage      <chr> "CodeCov", "CodeCov"
...