Bug#1142155: python3-vtk9: Syntax Warning during install

[SpikeTheHobbitMage at runbox.com]

Package: python3-vtk9
Version: 9.5.2+dfsg4-5+b2
Severity: minor
Tags: patch
X-Debbugs-Cc: SpikeTheHobbitMage at runbox.com

Python complains about a syntax error during installation.

```
/usr/lib/python3/dist-packages/vtkmodules/web/testing.py:687: SyntaxWarning: invalid escape sequence '\.'
  fnamePattern = re.compile("([^\.\/\\\]+)\.py")
/usr/lib/python3/dist-packages/vtkmodules/web/testing.py:687: SyntaxWarning: "\." is an invalid escape sequence. Such sequences will not work in the future. Did you mean "\\."? A raw string is also an option.
  fnamePattern = re.compile("([^\.\/\\\]+)\.py")
```

`"([^\.\/\\\]+)\.py"` isn't a valid string and the resulting regular expression only works by accident. It should be replaced with `r"([^./\\]+)\.py"` to get the intended behavior.

-- System Information:
Debian Release: forky/sid
  APT prefers testing
  APT policy: (990, 'testing'), (500, 'unstable'), (1, 'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 7.1.3+deb14-amd64 (SMP w/16 CPU threads; PREEMPT)
Locale: LANG=en_CA.UTF-8, LC_CTYPE=en_CA.UTF-8 (charmap=UTF-8), LANGUAGE=en_CA:en
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages python3-vtk9 depends on:
ii  libc6           2.42-17
ii  libgcc-s1       16.1.0-2
ii  libopenmpi40    5.0.10-1
ii  libpython3.14   3.14.6-1
ii  libstdc++6      16.1.0-2
ii  libtbb12        2022.3.0-2
ii  libvtk9.5       9.5.2+dfsg4-5+b2
ii  libvtk9.5-qt    9.5.2+dfsg4-5+b2
ii  python3         3.14.6-1
ii  python3-mpi4py  4.1.2-1

python3-vtk9 recommends no packages.

Versions of packages python3-vtk9 suggests:
pn  mayavi2        <none>
pn  vtk9-doc       <none>
pn  vtk9-examples  <none>

-- no debconf information