flatpak: quote python3-lsp pip command (YAML parsed ':all: ' as a mapping)

The unquoted build-command was parsed by YAML as a dict because of the
':all: ' colon-space, so flatpak-builder ran an empty module and pygls was
never installed into the bundle.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

package/flatpak/org.testium.Testium.yaml

@@ -40,7 +40,10 @@ modules:
       build-args:
         - --share=network
     build-commands:
-      - pip3 install --prefix=${FLATPAK_DEST} --only-binary=:all: "pygls>=1.3"
+      # Whole command single-quoted: the ':all: ' colon-space would otherwise
+      # make YAML parse this list item as a mapping, silently dropping the
+      # command (flatpak-builder then runs an empty module — installs nothing).
+      - 'pip3 install --prefix=${FLATPAK_DEST} --only-binary=:all: "pygls>=1.3"'
 
   # 1. Dépendances Python tierces (HORS PySide6)
   # Utilisez flatpak-pip-generator pour vos autres libs (ex: pyserial, requests, etc.)