test(data_dir): fix flaky getPlatformAppDataDir test on Windows

Delete the provided process.env.APPDATA on Windows, so that we can use our own values (one of which is "undefined", which was causing the getPlatformAppDataDir to fallback to the "real" process.env.APPDATA
-> causing failing test, when run on Windows

src/services/data_dir.spec.ts

@@ -77,6 +77,11 @@ describe("data_dir.ts unit tests", async () => {
             ["w/ darwin it should return '~/Library/Application Support'", ["darwin", undefined], "/Users/mock/Library/Application Support", "/Users/mock"]
         ];
 
+        beforeEach(() => {
+            // make sure OS does not set its own process.env.APPDATA, so that we can use our own supplied value
+            delete process.env.APPDATA;
+        });
+
         testCases.forEach((testCase) => {
             const [testDescription, fnValues, expected, osHomedirMockValue] = testCase;
             return it(testDescription, () => {