Read version file from base branch for version bumping

[Copilot]

Version bumping was reading from the PR branch, causing incorrect increments when the version had already been modified.

Changes

• lib/utils/bump.rb: Changed get_content_update to read version file content from @base_branch instead of @head_branch
• spec/lib/utils/bump_spec.rb: Updated tests to expect content sourced from base branch; removed duplicate test case

# Before
def get_content_update(path)
  head_branch_content = Content.new(config: @config, ref: @head_branch, path: path).content
  # ...
end

# After
def get_content_update(path)
  base_branch_content = Content.new(config: @config, ref: @base_branch, path: path).content
  # ...
end

Version increments now always calculate from the default branch state, regardless of PR branch modifications.

Original prompt

When bumping the version file, can you pull the version file from the default branch, instead of the current branch so that when you increment the version it is always the next version

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