Fix UpdateBuildNamesService to truncate build names before upsert

What does this MR do and why?

Fixes #583499

The Ci::UpdateBuildNamesService uses upsert_all to insert/update build names, which bypasses the Ci::BuildName model's name= setter that truncates values to 255 characters (MAX_JOB_NAME_LENGTH). This can lead to database constraint violations or inconsistent data when build names exceed the limit.

This MR ensures build names are truncated to MAX_JOB_NAME_LENGTH before being passed to upsert_all, maintaining data consistency and preventing potential database constraint violations.

How to set up and validate locally

1. Create a pipeline with a build that has a name longer than 255 characters
2. Run Ci::UpdateBuildNamesService.new(pipeline).execute
3. Verify that the build name in ci_build_names table is truncated to 255 characters

MR acceptance checklist

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Related issues

• Parent issue: #583031 (Database schema inconsistency for CI build name fields)