Add test demonstrating the problem with force-pushing in a triangular workflow

Our code doesn't realize that we need to prompt the user to force push, when the
branch is up-to-date with its upstream but not with the branch that we're
pushing to.

pkg/integration/tests/sync/force_push_triangular.go

@@ -0,0 +1,72 @@
+package sync
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+var ForcePushTriangular = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "Push to a remote, requiring a force push because the branch is behind the remote push branch but not the upstream",
+	ExtraCmdArgs: []string{},
+	Skip:         false,
+	GitVersion:   AtLeast("2.22.0"),
+	SetupConfig:  func(config *config.AppConfig) {},
+	SetupRepo: func(shell *Shell) {
+		shell.SetConfig("push.default", "current")
+
+		shell.EmptyCommit("one")
+
+		shell.CloneIntoRemote("origin")
+
+		shell.NewBranch("feature")
+		shell.SetBranchUpstream("feature", "origin/master")
+		shell.EmptyCommit("two")
+		shell.PushBranch("origin", "feature")
+
+		// remove the 'two' commit so that we are behind the push branch
+		shell.HardReset("HEAD^")
+	},
+	Run: func(t *TestDriver, keys config.KeybindingConfig) {
+		t.Views().Commits().
+			Lines(
+				Contains("one"),
+			)
+
+		t.Views().Status().Content(Contains("✓ repo → feature"))
+
+		t.Views().Files().IsFocused().Press(keys.Universal.Push)
+
+		// This results in an attempt to push normally, which fails with an error:
+		t.ExpectPopup().Alert().
+			Title(Equals("Error")).
+			Content(Contains("Updates were rejected. Please fetch and examine the remote changes before pushing again."))
+
+		/* EXPECTED:
+		t.ExpectPopup().Confirmation().
+			Title(Equals("Force push")).
+			Content(Equals("Your branch has diverged from the remote branch. Press <esc> to cancel, or <enter> to force push.")).
+			Confirm()
+
+		t.Views().Commits().
+			Lines(
+				Contains("one"),
+			)
+
+		t.Views().Status().Content(Contains("✓ repo → feature"))
+
+		t.Views().Remotes().Focus().
+			Lines(Contains("origin")).
+			PressEnter()
+
+		t.Views().RemoteBranches().IsFocused().
+			Lines(
+				Contains("feature"),
+				Contains("master"),
+			).
+			PressEnter()
+
+		t.Views().SubCommits().IsFocused().
+			Lines(Contains("one"))
+		*/
+	},
+})