Anchor VERSION match on the Docker epoch to avoid distro-version hits

[fudianchn]

Problem

On Ubuntu noble, VERSION=24.0 installs the latest Docker (28.4.0) instead of the requested 24.0 (#526):

INFO: apt-cache madison docker-ce | grep '24.0' | head -1 | ...

The grep matches VERSION anywhere in the madison line, so 24.0 matches the 24.04 in 5:28.4.0-1~ubuntu.24.04~noble, and head -1 then resolves to 28.4.0.

Fix

Anchor the grep on the Docker epoch (5:) so it matches the package version field (5:<version>-...) rather than the distro version embedded in the release suffix:

- search_command="apt-cache madison docker-ce     | grep '$pkg_pattern' | head -1 | ..."
+ search_command="apt-cache madison docker-ce     | grep '5:$pkg_pattern' | head -1 | ..."

Applied to both the docker-ce and docker-ce-cli lookups. Docker packages consistently use the 5: epoch, so this reliably binds the match to the version.

Verification

Simulated apt-cache madison docker-ce output (noble) with both 28.4.0 and 24.0.2 present, VERSION=24.0:

grep	selected (cut -f3)
grep '24.0' (before)	5:28.4.0-1~ubuntu.24.04~noble ← wrong (matched 24.04)
grep '5:24.0' (after)	5:24.0.2-1~ubuntu.24.04~noble ← correct

And when 24.0 is genuinely unavailable, grep '5:24.0' matches nothing → the script hits its existing ERROR: '$VERSION' not found amongst apt-cache madison results path and exits 1, instead of silently installing the latest.

bash -n install.sh passes.

Closes #526

[742764146]

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