maint(linux): ubuntu stonking support on launchpad is failing due to SHA1 signature

```
* Source Package: keyman
* Version: 19.0.271-1~sil1~stonking
* Architecture: arm64
* Archive: ~keymanapp/ubuntu/keyman-alpha
* Component: main
* State: Chroot problem
* Duration: 3 minutes
* Build Log: https://launchpad.net/~keymanapp/+archive/ubuntu/keyman-alpha/+build/33525334/+files/buildlog_ubuntu-stonking-arm64.keyman_19.0.271-1~sil1~stonking_BUILDING.txt.gz
* Builder: https://launchpad.net/builders/bos03-arm64-030
* Source: not available
```

## Error

```
Signing key on 6E03419649971F1382CE4AF4B033BBD612B4B657 is not bound: No binding signature at time 2026-08-20T19:49:51Z because: Policy rejected non-revocation signature (PositiveCertification) requiring second pre-image resistance because: SHA1 is not considered secure since 2026-02-01T00:00:00Z
```

## Full Build Log

```
https://launchpad.net/~keymanapp/+archive/ubuntu/keyman-alpha/+build/33525334
[Thu Aug 20 21:35:13 2026]
RUN: /usr/share/launchpad-buildd/bin/builder-prep
Kernel version: Linux bos03-arm64-030 6.8.0-136-generic #136-Ubuntu SMP PREEMPT_DYNAMIC Wed Jul 1 21:33:11 UTC 2026 aarch64
Buildd toolchain package versions: launchpad-buildd_266~799~ubuntu24.04.1 python3-lpbuildd_266~799~ubuntu24.04.1 sbuild_0.85.10ubuntu0.2 git-build-recipe_0.3.7 git_1:2.43.0-1ubuntu7.3 dpkg-dev_1.22.6ubuntu6.6 python3-debian_0.1.49ubuntu2.
Syncing the system clock with the buildd NTP service...
2026-08-20 21:35:13.459859 (+0000) -0.056906 +/- 0.059181 ntp.buildd 91.189.91.52 s3 no-leap
[Thu Aug 20 21:35:13 2026]
RUN: /usr/share/launchpad-buildd/bin/in-target unpack-chroot --backend=chroot --series=stonking --abi-tag=arm64 --isa-tag=arm64 PACKAGEBUILD-33525334 --image-type chroot /home/buildd/filecache-default/43651a6a861bb6b5717929083ec39ebb0f6606dc
Creating target for build PACKAGEBUILD-33525334
[Thu Aug 20 21:35:18 2026]
RUN: /usr/share/launchpad-buildd/bin/in-target mount-chroot --backend=chroot --series=stonking --abi-tag=arm64 --isa-tag=arm64 PACKAGEBUILD-33525334
Starting target for build PACKAGEBUILD-33525334
[Thu Aug 20 21:35:18 2026]
RUN: /usr/share/launchpad-buildd/bin/in-target override-sources-list --backend=chroot --series=stonking --abi-tag=arm64 --isa-tag=arm64 PACKAGEBUILD-33525334 'deb http://ppa.launchpadcontent.net/keymanapp/keyman-alpha/ubuntu stonking main' 'deb http://ftpmaster.internal/ubuntu stonking main restricted universe multiverse' 'deb http://ftpmaster.internal/ubuntu stonking-security main restricted universe multiverse' 'deb http://ftpmaster.internal/ubuntu stonking-updates main restricted universe multiverse'
Overriding sources.list in build-PACKAGEBUILD-33525334
[Thu Aug 20 21:35:19 2026]
RUN: /usr/share/launchpad-buildd/bin/in-target add-trusted-keys --backend=chroot --series=stonking --abi-tag=arm64 --isa-tag=arm64 PACKAGEBUILD-33525334
Adding trusted keys to build-PACKAGEBUILD-33525334
pub rsa4096/B033BBD612B4B657 2018-09-11 [SC]
Key fingerprint = 6E03 4196 4997 1F13 82CE 4AF4 B033 BBD6 12B4 B657
uid Launchpad PPA for Keyman for Linux

[Thu Aug 20 21:35:19 2026]
RUN: /usr/share/launchpad-buildd/bin/in-target update-debian-chroot --backend=chroot --series=stonking --abi-tag=arm64 --isa-tag=arm64 PACKAGEBUILD-33525334
Updating target for build PACKAGEBUILD-33525334
Get:1 http://ftpmaster.internal/ubuntu stonking InRelease [82.1 kB]
Get:2 http://ppa.launchpadcontent.net/keymanapp/keyman-alpha/ubuntu stonking InRelease [17.0 kB]
Err:2 http://ppa.launchpadcontent.net/keymanapp/keyman-alpha/ubuntu stonking InRelease
Sub-process /usr/bin/sqv returned an error code (1), error message is: Signing key on 6E03419649971F1382CE4AF4B033BBD612B4B657 is not bound: No binding signature at time 2026-08-20T19:49:51Z because: Policy rejected non-revocation signature (PositiveCertification) requiring second pre-image resistance because: SHA1 is not considered secure since 2026-02-01T00:00:00Z
Get:3 http://ftpmaster.internal/ubuntu stonking-security InRelease [60.7 kB]
Get:4 http://ftpmaster.internal/ubuntu stonking-updates InRelease [60.7 kB]
Get:5 http://ftpmaster.internal/ubuntu stonking/multiverse arm64 Packages [174 kB]
Get:6 http://ftpmaster.internal/ubuntu stonking/multiverse Translation-en [127 kB]
Get:7 http://ftpmaster.internal/ubuntu stonking/universe arm64 Packages [11.1 MB]
Get:8 http://ftpmaster.internal/ubuntu stonking/universe Translation-en [6579 kB]
Get:9 http://ftpmaster.internal/ubuntu stonking/main arm64 Packages [997 kB]
Get:10 http://ftpmaster.internal/ubuntu stonking/main Translation-en [525 kB]
Get:11 http://ftpmaster.internal/ubuntu stonking/restricted arm64 Packages [113 kB]
Get:12 http://ftpmaster.internal/ubuntu stonking/restricted Translation-en [26.4 kB]
Reading package lists...
W: Signature verification failed: http://ppa.launchpadcontent.net/keymanapp/keyman-alpha/ubuntu stonking InRelease: Sub-process /usr/bin/sqv returned an error code (1), error message is: Signing key on 6E03419649971F1382CE4AF4B033BBD612B4B657 is not bound: No binding signature at time 2026-08-20T19:49:51Z because: Policy rejected non-revocation signature (PositiveCertification) requiring second pre-image resistance because: SHA1 is not considered secure since 2026-02-01T00:00:00Z
E: The repository 'http://ppa.launchpadcontent.net/keymanapp/keyman-alpha/ubuntu stonking InRelease' is not signed.
Waiting 15 seconds and trying again ...
Get:1 http://ppa.launchpadcontent.net/keymanapp/keyman-alpha/ubuntu stonking InRelease [17.0 kB]
Err:1 http://ppa.launchpadcontent.net/keymanapp/keyman-alpha/ubuntu stonking InRelease
Sub-process /usr/bin/sqv returned an error code (1), error message is: Signing key on 6E03419649971F1382CE4AF4B033BBD612B4B657 is not bound: No binding signature at time 2026-08-20T19:49:51Z because: Policy rejected non-revocation signature (PositiveCertification) requiring second pre-image resistance because: SHA1 is not considered secure since 2026-02-01T00:00:00Z
Hit:2 http://ftpmaster.internal/ubuntu stonking InRelease
Hit:3 http://ftpmaster.internal/ubuntu stonking-security InRelease
Hit:4 http://ftpmaster.internal/ubuntu stonking-updates InRelease
Reading package lists...
W: Signature verification failed: http://ppa.launchpadcontent.net/keymanapp/keyman-alpha/ubuntu stonking InRelease: Sub-process /usr/bin/sqv returned an error code (1), error message is: Signing key on 6E03419649971F1382CE4AF4B033BBD612B4B657 is not bound: No binding signature at time 2026-08-20T19:49:51Z because: Policy rejected non-revocation signature (PositiveCertification) requiring second pre-image resistance because: SHA1 is not considered secure since 2026-02-01T00:00:00Z
E: The repository 'http://ppa.launchpadcontent.net/keymanapp/keyman-alpha/ubuntu stonking InRelease' is not signed.
Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/lpbuildd/target/apt.py", line 262, in run
self.backend.run(update_args, env=env, stdin=devnull)
File "/usr/lib/python3/dist-packages/lpbuildd/target/chroot.py", line 89, in run
subprocess.check_call(cmd, **kwargs)
File "/usr/lib/python3.12/subprocess.py", line 413, in check_call
raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['sudo', '/usr/sbin/chroot', '/home/buildd/build-PACKAGEBUILD-33525334/chroot-autobuild', 'linux64', 'env', 'LANG=C', 'DEBIAN_FRONTEND=noninteractive', 'TTY=unknown', '/usr/bin/apt-get', '-uy', 'update']' returned non-zero exit status 100.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/usr/share/launchpad-buildd/bin/in-target", line 20, in
sys.exit(main())
^^^^^^
File "/usr/share/launchpad-buildd/bin/in-target", line 16, in main
return args.operation.run()
^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3/dist-packages/lpbuildd/target/apt.py", line 266, in run
self.backend.run(update_args, env=env, stdin=devnull)
File "/usr/lib/python3/dist-packages/lpbuildd/target/chroot.py", line 89, in run
subprocess.check_call(cmd, **kwargs)
File "/usr/lib/python3.12/subprocess.py", line 413, in check_call
raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['sudo', '/usr/sbin/chroot', '/home/buildd/build-PACKAGEBUILD-33525334/chroot-autobuild', 'linux64', 'env', 'LANG=C', 'DEBIAN_FRONTEND=noninteractive', 'TTY=unknown', '/usr/bin/apt-get', '-uy', 'update']' returned non-zero exit status 100.
[Thu Aug 20 21:36:07 2026]
RUN: /usr/share/launchpad-buildd/bin/in-target scan-for-processes --backend=chroot --series=stonking --abi-tag=arm64 --isa-tag=arm64 PACKAGEBUILD-33525334
Scanning for processes to kill in build PACKAGEBUILD-33525334
```