Fix PURL for libwebp in qt_attribution.json


The version placeholder was malformed as "$v<VERSION>" instead of
"v$<VERSION>".

Pick-to: 6.5 6.8 6.11 6.12
Change-Id: I256a613ed7a607fed70638095943ea777557a961
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
commitc1a05e1d7717669e36807702e0f85958a1872556
parent7e7589f97f8190051c43b6afdee0c23937d6a1b6
authorKai Köhne <kai.koehne@qt.io>
committerKai Köhne <kai.koehne@qt.io>
commit timeTue, 11 Aug 2026 13:31:58 +0000