chore(release): prepare 1.4.0 for Jazzy and Humble

[xmfcx]

• Bump ros2_socketcan and ros2_socketcan_msgs from 1.3.0 to 1.4.0.
• Add concise release changelogs dated 2026-09-07, with a version-only entry for the unchanged message package.

Why

Prepare the source metadata for the 1.4.0 Bloom releases on Jazzy and Humble. The existing workflow mirrors pushes from jazzy to humble.

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Test plan

• git diff --check 9599ce5 6329ae9: no output and exit status 0.
• CI builds and tests after publication.

AI usage

AI usage: Codex ran catkin_generate_changelog, condensed its output, updated the package versions, and drafted this PR.

Self-review: It's alright.

Verification: XML and RST metadata checks passed for both packages on Ubuntu 24.04 with catkin_pkg 1.1.0. Package builds and runtime tests did not run.

Changelog generation

• catkin_generate_changelog exited with status 0 and updated two changelog files.

Release metadata checks

• Parsed two package manifests and two changelogs with catkin_pkg.
• Both package versions and latest changelog versions are 1.4.0.
• Both release dates are 2026-09-07.
• Prior changelog entries remain unchanged.
• The diff contains only four release metadata files: 4 files changed, 22 insertions(+), 2 deletions(-).
• Package builds, runtime tests, CI, and Bloom releases did not run.

Whitespace check

• git diff --check 9599ce5 6329ae9 produced no output and exited with status 0.