"mbsync gmail" unable to execute PassCmd

I have successfully used "mbsync" agains my gmail account, in Ubuntu 24.10, but in Ubuntu 25.04 this no longer works.
I have the following stanza in my ~/.mbsyncrc:
  PassCmd "/usr/bin/pass <email address hidden>"
This now results in mbsync terminating with error message:
(.venv) jw@SER8:~$ mbsync gmail
C: 0/1 B: 0/0 F: +0/0 *0/0 #0/0 N: +0/0 *0/0 #0/0
Skipping account gmail-remote, PassCmd failed: Permission denied

I have tried a number of different variations for this stanza, including specifying just the path to a shell-script taking no arguments.

If I instead specify the password in clear-text in .mbsyncrc, like this:
  Pass "1234 1234 1234 1234"
then I can successfully synchronize with gmail. But having the password in clear-text does not seem very secure.

I have now downloaded and built isync-1.5.1 from https://sourceforge.net/projects/isync/
This program appears to work correctly: I am now able to sync against gmail.

ProblemType: Bug
DistroRelease: Ubuntu 25.04
Package: isync 1.4.4-5build3
ProcVersionSignature: Ubuntu 6.14.0-15.15-generic 6.14.0
Uname: Linux 6.14.0-15-generic x86_64
ApportVersion: 2.32.0-0ubuntu5
Architecture: amd64
CasperMD5CheckResult: pass
CurrentDesktop: ubuntu:GNOME
Date: Sun May 18 10:51:07 2025
InstallationDate: Installed on 2024-12-11 (158 days ago)
InstallationMedia: Ubuntu 24.10 "Oracular Oriole" - Release amd64 (20241009.4)
ProcEnviron:
 LANG=en_US.UTF-8
 PATH=(custom, no user)
 SHELL=/bin/bash
 TERM=xterm-256color
 XDG_RUNTIME_DIR=<set>
SourcePackage: isync
UpgradeStatus: Upgraded to plucky on 2025-05-14 (4 days ago)