multi: context.Background() -> t.Context()

Use the new feature of Go 1.24, fix linter warnings.

This change was produced by:
 - running golangci-lint run --fix
 - sed 's/context.Background/t.Context/' -i `git grep -l context.Background | grep test.go`
 - manually fixing broken tests
 - itest, lntest: use ht.Context() where ht or hn is available
 - in HarnessNode.Stop() we keep using context.Background(), because it is
   called from a cleanup handler in which t.Context() is canceled already.

chanbackup/backup_test.go

@@ -121,8 +121,7 @@ func TestFetchBackupForChan(t *testing.T) {
 	}
 	for i, testCase := range testCases {
 		_, err := FetchBackupForChan(
-			context.Background(), testCase.chanPoint, chanSource,
-			chanSource,
+			t.Context(), testCase.chanPoint, chanSource, chanSource,
 		)
 		switch {
 		// If this is a valid test case, and we failed, then we'll
@@ -143,7 +142,7 @@ func TestFetchBackupForChan(t *testing.T) {
 // channel source for all channels and construct a Single for each channel.
 func TestFetchStaticChanBackups(t *testing.T) {
 	t.Parallel()
-	ctx := context.Background()
+	ctx := t.Context()
 
 	// First, we'll make the set of channels that we want to seed the
 	// channel source with. Both channels will be fully populated in the

chanbackup/pubsub_test.go

@@ -81,7 +81,7 @@ func (m *mockChannelNotifier) SubscribeChans(_ context.Context,
 // channel subscription, then the entire sub-swapper will fail to start.
 func TestNewSubSwapperSubscribeFail(t *testing.T) {
 	t.Parallel()
-	ctx := context.Background()
+	ctx := t.Context()
 
 	keyRing := &lnencrypt.MockKeyRing{}
 
@@ -159,7 +159,7 @@ func TestSubSwapperIdempotentStartStop(t *testing.T) {
 
 	swapper := newMockSwapper(keyRing)
 	subSwapper, err := NewSubSwapper(
-		context.Background(), nil, &chanNotifier, keyRing, swapper,
+		t.Context(), nil, &chanNotifier, keyRing, swapper,
 	)
 	require.NoError(t, err, "unable to init subSwapper")
 
@@ -226,8 +226,7 @@ func TestSubSwapperUpdater(t *testing.T) {
 	// With our channel set created, we'll make a fresh sub swapper
 	// instance to begin our test.
 	subSwapper, err := NewSubSwapper(
-		context.Background(), initialChanSet, chanNotifier, keyRing,
-		swapper,
+		t.Context(), initialChanSet, chanNotifier, keyRing, swapper,
 	)
 	require.NoError(t, err, "unable to make swapper")
 	if err := subSwapper.Start(); err != nil {