R version checks in `library()` cause warnings that fail tests on GLCI

[aitap]

Our periodic checks on platforms that use binary packages (Windows, macOS) started failing because the new version of bit64 was built on a newer R version than R-4.5.0:

Caught 1 warning outside the test() calls:
   after test                                         warning
        <num>                                          <char>
1:       2265 package 'bit64' was built under R version 4.5.3

with calls

test.data.table -> ... -> suppressPackageStartupMessages -> ... -> library -> testRversion -> warning

I'm not seeing a way to suppress the R_version_built_under > current check in the library function. Should we use suppressWarnings(suppressPackageStartupMessages(library(...)))? Is it worth asking on R-devel for a classed warning?