cmake: wrong project version propagated to pkg-config file

When building the project as:

mkdir build && cd build
cmake .. -DCMAKE_BUILD_TYPE=RELEASE

I get:

-- Opus library version: 0.8.0

-- Found Git: /usr/bin/git (found version "2.25.1")

-- Opus package version: 1.3.1

-- Opus project version: 1.3.1

the "Opus library version" is propagated in the pkg-config file (at the time of writing 0.8.0). I discovered this while building tag 1.3.1 locally. Including opus in my cmake project as pkg_check_modules(OPUS REQUIRED "opus") returned:

-- Found opus, version 0.8.0

I can live with it locally but I think it would good to fix it!