yum_src: use proper name variable name for "subprocess.TimeoutExpired"

[meaksh]

What does this PR change?

This PR simply fixes an small issue detected in a reference to subprocess.TimeoutExpired.

GUI diff

No difference.

• DONE

Documentation

• No documentation needed: only internal and user invisible changes

• DONE

Test coverage

• No tests: no tests around this feature

• DONE

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