note that 'Set Ltac Backtrace' is just a compat hack

tests/atomic.v

@@ -2,7 +2,7 @@ From iris.proofmode Require Import tactics.
 From iris.program_logic Require Export atomic.
 From iris.heap_lang Require Export lifting notation.
 From iris.heap_lang Require Import proofmode notation atomic_heap.
-Set Ltac Backtrace.
+Set Ltac Backtrace. (* FIXME: remove once we drop Coq 8.9 *)
 Set Default Proof Using "Type".
 
 Section tests.

tests/heap_lang.v

@@ -2,7 +2,7 @@ From iris.program_logic Require Export weakestpre total_weakestpre.
 From iris.heap_lang Require Import lang adequacy proofmode notation.
 (* Import lang *again*. This used to break notation. *)
 From iris.heap_lang Require Import lang.
-Set Ltac Backtrace.
+Set Ltac Backtrace. (* FIXME: remove once we drop Coq 8.9 *)
 Set Default Proof Using "Type".
 
 Section tests.

tests/proofmode.v

 From iris.proofmode Require Import tactics intro_patterns.
-Set Ltac Backtrace.
+Set Ltac Backtrace. (* FIXME: remove once we drop Coq 8.9 *)
 Set Default Proof Using "Type".
 
 Section tests.

tests/proofmode_iris.v

 From iris.proofmode Require Import tactics monpred.
 From iris.base_logic Require Import base_logic.
 From iris.base_logic.lib Require Import invariants cancelable_invariants na_invariants.
-Set Ltac Backtrace.
+Set Ltac Backtrace. (* FIXME: remove once we drop Coq 8.9 *)
 
 Section base_logic_tests.
   Context {M : ucmraT}.

tests/proofmode_monpred.v

 From iris.proofmode Require Import tactics monpred.
 From iris.base_logic.lib Require Import invariants.
-Set Ltac Backtrace.
+Set Ltac Backtrace. (* FIXME: remove once we drop Coq 8.9 *)
 
 Section tests.
   Context {I : biIndex} {PROP : sbi}.

tests/proofmode_siprop.v

 From iris.proofmode Require Import tactics .
 From iris.si_logic Require Import bi.
-Set Ltac Backtrace.
+Set Ltac Backtrace. (* FIXME: remove once we drop Coq 8.9 *)
 
 Section si_logic_tests.
   Implicit Types P Q R : siProp.