Fixes spurious error messages in tests

Previously, `isAnalyzingDefaultBranch` was failing because there are
some missing env vars: `GITHUB_SHA`, `GITHUB_REF`, and
`GITHUB_EVENT_PATH`. Also, `checkout_path` is missing as an input.

Rather than trying to set them to mock values, which would require
setting the paths to existing paths in the file system, I chose to stub
the entire function. I think this is fine since the point of the test
is to check the ram and threads values, not testing the
`isAnalyzingDefaultBranch` function.

src/analyze-action-env.test.ts

@@ -29,6 +29,8 @@ test("analyze action with RAM & threads from environment variables", async (t) =
       .stub(actionsUtil, "createStatusReportBase")
       .resolves({} as actionsUtil.StatusReportBase);
     sinon.stub(actionsUtil, "sendStatusReport").resolves(true);
+    sinon.stub(actionsUtil, "isAnalyzingDefaultBranch").resolves(true);
+
     const gitHubVersion: util.GitHubVersion = {
       type: util.GitHubVariant.DOTCOM,
     };

src/analyze-action-input.test.ts

@@ -45,6 +45,7 @@ test("analyze action with RAM & threads from action inputs", async (t) => {
     optionalInputStub.withArgs("cleanup-level").returns("none");
     optionalInputStub.withArgs("expect-error").returns("false");
     sinon.stub(util, "getGitHubVersion").resolves(gitHubVersion);
+    sinon.stub(actionsUtil, "isAnalyzingDefaultBranch").resolves(true);
     setupActionsVars(tmpDir, tmpDir);
     mockFeatureFlagApiEndpoint(200, {});