Reduce the scope of stackTrace var (#5583)

Fixes #5571.

lib/pure/unittest.nim

@@ -375,7 +375,6 @@ template test*(name, body) {.dirty.} =
   ensureFormattersInitialized()
 
   if shouldRun(name):
-    var stackTrace {.inject.}: string
     checkpoints = @[]
     var testStatusIMPL {.inject.} = OK
 
@@ -391,7 +390,7 @@ template test*(name, body) {.dirty.} =
     except:
       when not defined(js):
         checkpoint("Unhandled exception: " & getCurrentExceptionMsg())
-        stackTrace = getCurrentException().getStackTrace()
+        var stackTrace {.inject.} = getCurrentException().getStackTrace()
       fail()
 
     finally:

tests/stdlib/tunittest.nim

@@ -96,5 +96,12 @@ suite "bug #4494":
       check:
         allIt(0..3, tags[it] != tags[it + 1])
 
+suite "bug #5571":
+  test "can define gcsafe procs within tests":
+    proc doTest {.gcsafe.} =
+      let line = "a"
+      check: line == "a"
+    doTest()
+
 static:
   echo "compile end"