invoices: use longer timeout for HTLC resolution in AMP test

Under parallel Postgres test load, the event loop must complete
sequential DB writes after SetTime fires. Using testTimeout (5s)
is too tight; switch the three blocking hodlChan selects in
testFailPartialAMPPayment to testTimeoutLong (1 minute) to
match the pattern already used elsewhere for slow backends.

invoices/invoiceregistry_test.go

@@ -2322,7 +2322,7 @@ func testFailPartialAMPPayment(t *testing.T,
 			"expected MPPTimeout, got: %v", failRes.Outcome,
 		)
 
-	case <-time.After(testTimeout):
+	case <-time.After(testTimeoutLong):
 		t.Fatal("timeout waiting for HTLC resolution")
 	}
 
@@ -2339,7 +2339,7 @@ func testFailPartialAMPPayment(t *testing.T,
 			"expected MPPTimeout, got: %v", failRes.Outcome,
 		)
 
-	case <-time.After(testTimeout):
+	case <-time.After(testTimeoutLong):
 		t.Fatal("timeout waiting for HTLC resolution")
 	}
 
@@ -2408,7 +2408,7 @@ func testFailPartialAMPPayment(t *testing.T,
 			"expected MPPTimeout, got: %v", failRes.Outcome,
 		)
 
-	case <-time.After(testTimeout):
+	case <-time.After(testTimeoutLong):
 		t.Fatal("timeout waiting for HTLC resolution")
 	}