Refresh apt indexes before CI and Docker dependency installs

[yeseorizi]

Summary

• refresh the Ubuntu/ROS apt indexes immediately before rosdep install in both Dockerfiles
• install the GitHub lint runner system dependencies after an explicit apt-get update
• keep XML lint tools in the same system-dependency installation step

Why

The release-candidate ARM64 build initially failed because a cached apt index referenced rotated ROS 2 Lyrical package files and returned HTTP 404. The lint workflow failed for the same reason while installing libxml2-utils. Refreshing the indexes at the point of use prevents cached Docker layers and hosted-runner package lists from becoming stale.

Validation

• reproduced the stale-index 404 failure
• retried the ARM64 Docker build with this change
• ROS dependencies installed successfully with the current package versions
• all 14 DAVE workspace packages compiled successfully in the ARM64 image build
• git diff --check passed

Full image assembly and Quickstart validation are being recorded separately as release-candidate evidence.

[yeseorizi]

Final local merge-candidate validation

I applied this PR's patch to a local candidate based on ros2@492e926 with PRs #66, #67, #68, #69, and #70 integrated. PR #44 was intentionally excluded because it is still unmerged.

Results on native Apple M2 / linux/arm64:

• Full ARM64 Docker build: PASS
• DAVE colcon workspace: 14/14 packages built
• ArduSub SITL and ardupilot_gazebo: built successfully
• GeographicLib dataset check: PASS
• Public executable Quickstarts: 14/14 PASS
• All 14 launches produced simulation statistics and satisfied their entity/topic oracles
• Graceful shutdown: 14/14, with forced_kill=0

Built image ID: sha256:b5e3079ff57d892b0265fc63fc230ae70887c388c53d27a729e0cbf4091ff701 (linux/arm64).

The initial build reproduced the stale apt-index HTTP 404; after applying this PR, the full build and runtime suite completed successfully. This is a local pre-merge candidate result, not a claim about the official ros2 branch or Docker Hub push.