Cirrus CI: Don't allow macOS arm64 jobs to fail anymore (#4400)

As there's a single remaining failure - `runnable/test34.d` fails,
with enabled optimizations only.

.cirrus.yml

@@ -289,7 +289,6 @@ task:
 
 task:
   name: macOS 12 $TASK_NAME_SUFFIX
-  allow_failures: true # FIXME
   macos_instance:
     image: ghcr.io/cirruslabs/macos-monterey-xcode:latest
   timeout_in: 25m

tests/dmd/runnable/test34.d

@@ -612,6 +612,8 @@ void test33()
 
 /************************************************/
 
+version (LDC) version (D_Optimized) version (darwin) version (AArch64) version = LDC_Optimized_Apple_AArch64;
+
 struct Vector34
 {
     float x, y, z;
@@ -679,6 +681,7 @@ class Foo34
     private void bar()
     {
         auto s = foobar();
+        version (LDC_Optimized_Apple_AArch64) { /* FIXME */ } else
         assert(format34("%s", s) == "<1.000000, 0.000000, 0.000000>");
     }