Call me naive (I don't use arch) but if that's the only change then what's the point releasing the change? Unless pkgver refers to an external dependency or a binary, in which case you might as well say reading the changelog counts as reading the code

Usually you concat them to form the GitHub tarball URL or similar, so on updates you only review the version/hash bumps, as on install you've validated the right GitHub organization/domain already.

Babashka has this for example (https://aur.archlinux.org/cgit/aur.git/tree/PKGBUILD?h=babas...):

    pkgname=babashka-bin
    pkgver=1.13.219
    url='https://github.com/borkdude/babashka'
    source_x86_64=("${pkgname}-${pkgver}-linux-amd64-static.tar.gz::${url}/releases/download/v${pkgver}/${pkgname%-bin}-${pkgver}-linux-amd64-static.tar.gz")

AUR packages consist of packaging a third-party software (whether binary or source built as part of the package) for use on Arch.

Most updates are just bumping the upstream software version and its checksum, as GP describes, and yes arguably you should be reviewing the change to that software too, but that's a separate threat. And it may be a proprietary binary, in which case on update you've already decided to trust the third-party, so the diff shows you that nothing has changed in that regard, the trusted party simply released a new opaque version.