validation: install the wheel with the [lsp] extra in wheel mode

The wheel channel was installed without [lsp], so 'testium lsp' reported pygls
missing. Install testium[lsp] in the wheel venv — validating the wheel's
language-server-capable form, like the AppImage installs ...whl[lsp].

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

test/validation/run.sh

@@ -97,7 +97,10 @@ case "$MODE" in
             echo "Creating wheel venv at $WHEEL_VENV"
             python3 -m venv --system-site-packages "$WHEEL_VENV"
             "$WHEEL_VENV/bin/pip" install --quiet --upgrade pip
-            "$WHEEL_VENV/bin/pip" install --quiet "$WHEEL"
+            # Install with the [lsp] extra so the wheel channel is validated in
+            # its language-server-capable form (pulls pygls), matching how a
+            # user enables `testium lsp` from a wheel: pip install testium[lsp].
+            "$WHEEL_VENV/bin/pip" install --quiet "${WHEEL}[lsp]"
         fi
         CMD=("$WHEEL_VENV/bin/python" -m testium)
         ;;