Provide a way for Voici to pin packages (#139)

* Provide a way for Voici to pin packages

* Fix Python version

Author: martinRenou

.github/workflows/build.yml

@@ -55,7 +55,7 @@ jobs:
       - name: Install Python
         uses: actions/setup-python@v2
         with:
-          python-version: '3.8'
+          python-version: '3.10'
           architecture: 'x64'
       - uses: actions/download-artifact@v2
         with:

.github/workflows/check-release.yml

@@ -19,7 +19,7 @@ jobs:
       - name: Install Python
         uses: actions/setup-python@v2
         with:
-          python-version: 3.9
+          python-version: '3.10'
           architecture: 'x64'
       - name: Install node
         uses: actions/setup-node@v2

jupyterlite_xeus_python/env_build_addon.py

@@ -52,6 +52,10 @@ class XeusPythonEnv(FederatedExtensionAddon):
         description="The path or URL to the empack config file",
     )
 
+    pin_packages = PackagesList([]).tag(
+        description="This property is not supposed to be used, unless you know what you're doing.",
+    )
+
     packages = PackagesList([]).tag(
         config=True,
         description="A comma-separated list of packages to install in the xeus-python env",
@@ -78,7 +82,7 @@ def post_build(self, manager):
 
         env_prefix = build_and_pack_emscripten_env(
             xeus_python_version=self.xeus_python_version,
-            packages=self.packages,
+            packages=[*self.packages, *self.pin_packages],
             environment_file=Path(self.manager.lite_dir) / self.environment_file,
             empack_config=self.empack_config,
             output_path=self.cwd.name,