Make sure IFileSystem is registered in DI during tests. (#8902)

(for #8882)

Author: ericsnowcurrently

.gitignore

@@ -39,3 +39,7 @@ tmp/**
 test-results.xml
 uitests/out/**
 !build/
+
+# TODO (GH-8925) This is temporary.  We will remove it when we adjust
+# tests to not leave the file behind.
+src/test/get-pip.py

src/test/debugger/envVars.test.ts

@@ -49,6 +49,7 @@ suite('Resolving Environment Variables when Debugging', () => {
     function initializeDI() {
         ioc = new UnitTestIocContainer();
         ioc.registerProcessTypes();
+        ioc.registerFileSystemTypes();
         ioc.registerVariableTypes();
         ioc.registerMockProcess();
     }