use !r instead of lengthy function call

pre_commit/languages/r.py

@@ -92,9 +92,7 @@ def install_environment(
         cmd_output_b(
             'Rscript', '--vanilla', '-e',
             f"""\
-            prefix_dir <- "{
-                prefix.prefix_dir.encode('unicode_escape').decode()
-            }"
+            prefix_dir <- {prefix.prefix_dir!r}
             missing_pkgs <- setdiff(
                 "renv", unname(installed.packages()[, "Package"])
             )