unbreq plugin: unify output format

[mkoncek]

label no-release-notes

Let's use one log event per one BuildRequires field consistently.

[gemini-code-assist]

Code Review

This pull request refactors the logging output for the unbreq plugin to be more consistent by logging one event per BuildRequires field. The changes are clear and effectively achieve this goal. I have added a couple of suggestions to use f-strings for the new log messages to align with the prevailing style in the codebase, which should also improve readability.

[gemini-code-assist]

For consistency with the rest of the codebase, which already uses f-strings, consider converting this log message to use an f-string. This improves readability by embedding expressions directly inside the string literal.

Suggested change

	"unbreq plugin: BuildRequires '%s' is needed because file %s was accessed",
	br, short_path
	f"unbreq plugin: BuildRequires '{br}' is needed "
	f"because file {short_path} was accessed"