Add Cargo.lock to the repository

This makes sure that any broken dependency updates are not breaking our
build, at the cost of requiring us to update the lock file regularly.

See also https://blog.rust-lang.org/2023/08/29/committing-lockfiles.html

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer-rs/-/merge_requests/1340>

.gitlab-ci.yml

@@ -95,13 +95,6 @@ trigger:
   before_script:
     - source ./ci/env.sh
     - mkdir .cargo && echo -e "[net]\ngit-fetch-with-cli = true" > .cargo/config
-    # If cargo exists assume we probably will want to update
-    # the lockfile
-    - |
-      if command -v cargo; then
-        cargo generate-lockfile --color=always
-        cargo update --color=always
-      fi
 
 .debian:12-base:
   extends: .debian:12