ci(image): install PyICU so gramps' webreport module is importable

The integration lane reported TimePedigreeHTML as a failed-to-load addon
(NameError: name 'localAlphabeticIndex' is not defined). The defect is not in
the addon: gramps 6.0's gramps/plugins/webreport/common.py sets

    HAVE_ICU = False
    try:    from icu import Locale ...
    except ImportError:
        try:    from PyICU import Locale ...
        except ImportError:  pass      # <- nothing imported at all

and later does 'else: AlphabeticIndex = localAlphabeticIndex' — a name only
bound on the inner fallback paths. With NEITHER icu nor PyICU installed the
module raises NameError at import, so every addon importing it fails to load.
The CI image had no PyICU (the logs were full of 'ICU not loaded ...
Localization will be impaired'), so CI was reporting an addon defect that does
not exist for real users, who normally have PyICU.

Install PyICU (and libicu-dev to build it). This fixes the false addon
failure, silences the localization warnings, and makes the image represent a
realistic Gramps environment. The underlying gramps guard is still wrong and
worth reporting upstream.

Author: eduralph

.github/docker/gramps-ci/Dockerfile

@@ -67,6 +67,7 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
         pkg-config \
         python3-dev \
         libcairo2-dev \
+        libicu-dev \
         intltool \
         gettext \
         git \
@@ -82,7 +83,18 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 # ruff is PINNED: an unpinned ruff would change the lint verdict on rebuild (a
 # new rule in the E9/F63/F7/F82 selection flips a lane red — or silently stops
 # flagging — with no repo change). Bump deliberately, not by rebuild drift.
-RUN pip install --no-cache-dir PyGObject pycairo orjson ruff==0.15.22
+#
+# PyICU is REQUIRED, not optional. Gramps degrades localization without it
+# ("ICU not loaded ... Localization will be impaired"), and worse, gramps 6.0's
+# gramps/plugins/webreport/common.py cannot even be IMPORTED without it: when
+# neither `icu` nor `PyICU` resolves, its outer `except ImportError: pass`
+# leaves `localAlphabeticIndex` unbound and the module-level
+# `AlphabeticIndex = localAlphabeticIndex` raises NameError. Every addon that
+# imports that module (e.g. TimePedigreeHTML) then fails to load, so CI without
+# PyICU reports an addon defect that does not exist for real users. Installing
+# it also makes the image match a normal Gramps environment. (Built from source
+# against libicu-dev above.)
+RUN pip install --no-cache-dir PyGObject pycairo orjson PyICU ruff==0.15.22
 
 # Install gramps: PyPI first, SHA-pinned git clone as fallback.
 RUN /bin/bash -eo pipefail <<'BASH'