Fetch only default branch when syncing the fork (#938)

* Fetch only default branch when syncing the fork

The default branch is the only branch required from the upstream repo
for syncing Scala Steward's fork. Working on large repos with many
branches will be a lot faster with this change.

* Update tests

Author: fthomas

modules/core/src/main/scala/org/scalasteward/core/git/GitAlg.scala

@@ -171,7 +171,7 @@ object GitAlg {
           branch = defaultBranch.name
           remoteBranch = s"$remote/$branch"
           _ <- exec(Nel.of("remote", "add", remote, upstreamUrl.toString), repoDir)
-          _ <- exec(Nel.of("fetch", remote), repoDir)
+          _ <- exec(Nel.of("fetch", remote, branch), repoDir)
           _ <- exec(Nel.of("checkout", "-B", branch, "--track", remoteBranch), repoDir)
           _ <- exec(Nel.of("merge", remoteBranch), repoDir)
           _ <- push(repo, defaultBranch)

modules/core/src/test/scala/org/scalasteward/core/git/GitAlgTest.scala

@@ -89,7 +89,7 @@ class GitAlgTest extends AnyFunSuite with Matchers {
           "upstream",
           "http://github.com/fthomas/datapackage"
         ),
-        List(askPass, repoDir, "git", "fetch", "upstream"),
+        List(askPass, repoDir, "git", "fetch", "upstream", "master"),
         List(askPass, repoDir, "git", "checkout", "-B", "master", "--track", "upstream/master"),
         List(askPass, repoDir, "git", "merge", "upstream/master"),
         List(askPass, repoDir, "git", "push", "--force", "--set-upstream", "origin", "master")

modules/core/src/test/scala/org/scalasteward/core/github/GitHubRepoAlgTest.scala

@@ -74,7 +74,7 @@ class GitHubRepoAlgTest extends AnyFunSuite with Matchers {
           "upstream",
           s"https://${config.vcsLogin}@github.com/fthomas/datapackage"
         ),
-        List(askPass, repoDir, "git", "fetch", "upstream"),
+        List(askPass, repoDir, "git", "fetch", "upstream", "master"),
         List(askPass, repoDir, "git", "checkout", "-B", "master", "--track", "upstream/master"),
         List(askPass, repoDir, "git", "merge", "upstream/master"),
         List(askPass, repoDir, "git", "push", "--force", "--set-upstream", "origin", "master")