refactor: remove unnecessary if from git.setBranch (#6815)

Co-authored-by: Michael Kriese <michael.kriese@visualon.de>

lib/util/git/index.spec.ts

@@ -114,6 +114,9 @@ describe('platform/git', () => {
     });
   });
   describe('isBranchStale()', () => {
+    beforeEach(async () => {
+      await git.setBranch('master');
+    });
     it('should return false if same SHA as master', async () => {
       expect(await git.isBranchStale('renovate/future_branch')).toBe(false);
     });

lib/util/git/index.ts

@@ -308,22 +308,19 @@ export async function getCommitMessages(): Promise<string[]> {
 }
 
 export async function setBranch(branchName: string): Promise<string> {
-  if (branchName) {
   if (!(await branchExists(branchName))) {
     throwBranchValidationError(branchName);
   }
   logger.debug(`Setting current branch to ${branchName}`);
-    config.currentBranch = branchName;
   try {
-      if (branchName !== 'master') {
+    config.currentBranch = branchName;
     config.currentBranchSha = (
       await git.raw(['rev-parse', 'origin/' + branchName])
     ).trim();
-      }
     await git.checkout([branchName, '-f']);
-      await git.reset(ResetMode.HARD);
     const latestCommitDate = (await git.log({ n: 1 })).latest.date;
     logger.debug({ branchName, latestCommitDate }, 'latest commit');
+    await git.reset(ResetMode.HARD);
   } catch (err) /* istanbul ignore next */ {
     checkForPlatformFailure(err);
     if (
@@ -336,7 +333,6 @@ export async function setBranch(branchName: string): Promise<string> {
     }
     throw err;
   }
-  }
   return (
     config.currentBranchSha ||
     (await git.raw(['rev-parse', 'origin/master'])).trim()
@@ -396,7 +392,7 @@ export async function isBranchStale(branchName: string): Promise<boolean> {
     '--remotes',
     '--verbose',
     '--contains',
-    config.currentBranchSha || `origin/${config.currentBranch}`,
+    config.currentBranchSha,
   ]);
   return !branches.all.map(localName).includes(branchName);
 }