Fix CI for MW master: tolerate absent Wikibase JS submodules

The MW master CI job aborted in installMediaWiki.sh with exit 128:

    fatal: no submodule mapping found in .gitmodules for path 'view/lib/wikibase-serialization'

Wikibase master removed the wikibase-serialization, wikibase-data-values and
wikibase-data-model view-layer submodules (migrated to npm), so `git submodule
set-url` on those paths fails. Under `set -e` this aborted the install before
PHPUnit ran, and fail-fast then cancelled every other matrix job.

These JS libraries are not needed by the PHP test suite. Make the URL rewrites
tolerant of an absent submodule so the script no longer aborts on master, while
behaviour on REL1_43/44/45 (where the submodules still exist) is unchanged.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: JeroenDeDauw

.github/workflows/installMediaWiki.sh

@@ -60,9 +60,15 @@ cd extensions
 git clone https://gerrit.wikimedia.org/r/mediawiki/extensions/Elastica --depth=1  --branch=$MW_BRANCH --recurse-submodules -j8
 git clone https://gerrit.wikimedia.org/r/mediawiki/extensions/CirrusSearch --depth=1  --branch=$MW_BRANCH --recurse-submodules -j8
 
-git clone https://gerrit.wikimedia.org/r/mediawiki/extensions/Wikibase --depth=1 --branch=$MW_BRANCH -j8 && \
-  cd Wikibase && \
-  git submodule set-url view/lib/wikibase-serialization https://github.com/wmde/WikibaseSerializationJavaScript.git && \
-  git submodule set-url view/lib/wikibase-data-values https://github.com/wmde/DataValuesJavaScript.git && \
-  git submodule set-url view/lib/wikibase-data-model https://github.com/wmde/WikibaseDataModelJavaScript.git && \
-  git submodule sync && git submodule init && git submodule update --recursive
+git clone https://gerrit.wikimedia.org/r/mediawiki/extensions/Wikibase --depth=1 --branch=$MW_BRANCH -j8
+cd Wikibase
+
+# The wikibase-serialization, wikibase-data-values and wikibase-data-model submodules point at
+# Phabricator URLs that are unreliable in CI, so rewrite them to GitHub mirrors. These submodules
+# only exist on the REL branches; MediaWiki master removed them (migrated to npm), so skip silently
+# when absent instead of aborting the build.
+git submodule set-url view/lib/wikibase-serialization https://github.com/wmde/WikibaseSerializationJavaScript.git 2>/dev/null || true
+git submodule set-url view/lib/wikibase-data-values https://github.com/wmde/DataValuesJavaScript.git 2>/dev/null || true
+git submodule set-url view/lib/wikibase-data-model https://github.com/wmde/WikibaseDataModelJavaScript.git 2>/dev/null || true
+
+git submodule sync && git submodule init && git submodule update --recursive