close #10307(add testcase for #10307) (#15840)

(cherry picked from commit dfa2f011d7)

tests/magics/t10307.nim

@@ -0,0 +1,23 @@
+discard """
+  cmd: "nim c -d:useGcAssert $file"
+  output: '''running someProc(true)
+res: yes
+yes
+running someProc(false)
+res:
+'''
+"""
+
+proc someProc(x:bool):cstring =
+  var res:string = ""
+  if x:
+    res = "yes"
+  echo "res: ", res
+  GC_ref(res)
+  result = res
+
+echo "running someProc(true)"
+echo someProc(true)
+
+echo "running someProc(false)"
+echo someProc(false)