I re-ran with -K (e.g. guix pull -v3 --commit 2641621 -K 2>&1 | tee guix-pull-bug-verbose-02) to keep build files, and a quick cat /tmp/guix-build-util-linux-2.37.2.drv-0/util-linux-2.37.2/tests/output/misc/swaplabel.err appears to confirm the bug
mkswap: error: swap area needs to be at least 10 pages
mkswap: <swapfile>: insecure permissions <perm>, fix with: chmod 0600 <swapfile>
mkswap: <swapfile> contains holes or other unsupported extents.
This swap file can be rejected by kernel on swap activation!
Use --verbose for more details.
mkswap: Label was truncated.
I'm still green to know how to fix this, but I presume if I check out the latest version via git and the docs online, I should be able to update the definition for util-linux to include the patch, then try again?