fix(gazelle): Fix the requirements arg to the gazelle python manifest generator. (#2533)

Fix args passed into the gazelle manifest file generator if the
requirements file is not a source file.

---------

Co-authored-by: Douglas Thor <dougthor42@users.noreply.github.com>

CHANGELOG.md

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6ccc568..7f4c60b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,7 +4,7 @@
 # rules_python Changelog
 
 This is a human-friendly changelog in a keepachangelog.com style format.
-Because this changelog is for end-user consumption of meaningful changes,only
+Because this changelog is for end-user consumption of meaningful changes, only
 a summary of a release's changes is described. This means every commit is not
 necessarily mentioned, and internal refactors or code cleanups are omitted
 unless they're particularly notable.
@@ -56,7 +56,7 @@
 
 {#v0-0-0-fixed}
 ### Fixed
-* Nothing fixed.
+* (gazelle) Providing multiple input requirements files to `gazelle_python_manifest` now works correctly.
 
 {#v0-0-0-added}
 ### Added

gazelle/manifest/defs.bzl

diff --git a/gazelle/manifest/defs.bzl b/gazelle/manifest/defs.bzl
index 3a65bff..6c0072a 100644
--- a/gazelle/manifest/defs.bzl
+++ b/gazelle/manifest/defs.bzl
@@ -79,7 +79,7 @@
 
     update_args = [
         "--manifest-generator-hash=$(execpath {})".format(manifest_generator_hash),
-        "--requirements=$(rootpath {})".format(requirements) if requirements else "--requirements=",
+        "--requirements=$(execpath {})".format(requirements) if requirements else "--requirements=",
         "--pip-repository-name={}".format(pip_repository_name),
         "--modules-mapping=$(execpath {})".format(modules_mapping),
         "--output=$(execpath {})".format(generated_manifest),