Do proper path join for strip_prefix

In some cases there's a `/` at the end of `bin_dir.path` and in some
cases there isn't.  Using `paths.join()` should deal properly with
both cases.

Author: kellyma2

internal/rpmtree.bzl

@@ -19,6 +19,7 @@ rpm files into either a .tar or extract files from that tar to
 make available to bazel
 """
 
+load("@bazel_skylib//lib:paths.bzl", "paths")
 load("//bazeldnf:toolchain.bzl", "BAZELDNF_TOOLCHAIN")
 load("//internal:rpm.bzl", "RpmInfo")
 
@@ -72,7 +73,11 @@ def _expand_path(files):
 
 def _tar2files_impl(ctx):
     args = ctx.actions.args()
-    strip_prefix = ctx.bin_dir.path + ctx.label.package + "/" + ctx.label.name
+    strip_prefix = paths.join(
+        ctx.bin_dir.path,
+        ctx.label.package,
+        ctx.label.name,
+    )
 
     args.set_param_file_format("multiline")
     args.use_param_file("@%s")