Build issue when building using m2Local support + pinning

[oliviernotteghem]

Error is observed when building an (android) project using local artifact (via 'm2Local' reprository) and pinning.

Repro:

1. Unzip androidx.zip into~/.m2/repository folder.
2. Clone https://github.com/oliviernotteghem/rules_jvm_external which contains this commit
3. cd examples/android_kotlin_app
4. rm -rf <path to repo cache, ex : /private/var/tmp/_bazel_oliviern/cache/repos/v1>; bazel clean --expunge; bazel build app

Result:
ERROR: /private/var/tmp/_bazel_oliviern/d757db415344097304197092f16ed4d8/external/maven/BUILD:9:11: Stamping the manifest of @maven//:androidx_annotation_annotation failed: missing input file '@maven//:androidx/annotation/annotation/1.5.0-LOCAL/annotation-1.5.0-LOCAL.jar'

Note:
When building without pinning, builds succeeds.

It looks like the issue is due to the symlink from the absolute path of the artifact to the relative path within the output_base/external for local artifact gets wipeout at the beginning of build when pinning is used (i.e maven_install_json attribute is specified)

[oliviernotteghem]

Possible fix :

def extract_netrc_from_auth_url(url):
    """Return a dict showing the netrc machine, login, and password extracted from a url.
@@ -1005,7 +1005,7 @@ def _coursier_fetch_impl(repository_ctx):
            # b) Otherwise, we clear the url and also simlink the file from the maven local directory
            #    to file within the repository rule workspace
            print("Assuming maven local for artifact: %s" % artifact["coord"])
-            artifact.update({"url": None})
+            artifact.update({"url": "file://" + artifact["file"]})
            if not repository_ctx.attr.name.startswith("unpinned_"):
                artifact.update({"file": _relativize_and_symlink_file_in_maven_local(repository_ctx, artifact["file"])})

[gergelyfabian]

artifact.update({"url": "file://" + artifact["file"]})

Tried applying this fix, but it did not work.
Works with the version from the PR #961.