Don't warn about missing .py files in VS Code

Our _pb2.py files are available at runtime, and we only need the .pyi
files for editing.

.vscode/settings.json

@@ -9,6 +9,9 @@
     "python.analysis.extraPaths": ["./pylib"],
     "python.formatting.provider": "black",
     "python.linting.mypyEnabled": false,
+    "python.analysis.diagnosticSeverityOverrides": {
+        "reportMissingModuleSource": "none"
+    },
     "rust-analyzer.cargo.runBuildScripts": true,
     "rust-analyzer.checkOnSave.allTargets": false,
     "rust-analyzer.files.excludeDirs": [".bazel", "node_modules"],