test: Add one more br_if test case

[chfast]

Idea taken from #367 (comment).

This seems to be running slightly slower, so leaving only tests case.
Diff for reference:

--- a/lib/fizzy/execute.cpp
+++ b/lib/fizzy/execute.cpp
@@ -678,20 +678,19 @@ execution_result execute(
                 goto end;
             break;
         }
-        case Instr::br:
+
         case Instr::br_if:
-        case Instr::return_:
-        {
-            // Check condition for br_if.
-            if (instruction == Instr::br_if && static_cast<uint32_t>(stack.pop()) == 0)
+            if (static_cast<uint32_t>(stack.pop()) == 0)
             {
                 immediates += BranchImmediateSize;
                 break;
             }
-
+            [[fallthrough]];
+        case Instr::br:
+        case Instr::return_:
             branch(code, stack, pc, immediates);
             break;
-        }
+
         case Instr::br_table:
         {
             const auto br_table_size = read<uint32_t>(immediates);

[codecov]

Codecov Report

Merging #378 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #378   +/-   ##
=======================================
  Coverage   99.32%   99.32%           
=======================================
  Files          42       42           
  Lines       12814    12834   +20     
=======================================
+ Hits        12728    12748   +20     
  Misses         86       86