[flang][test] Change re.I to flags=re.I in re.sub

Follow-up to da6099c. As a positional argument, the `re.I` was in
place of `count`, not `flags`.

Author: kparzysz

flang/test/Semantics/test_symbols.py

@@ -29,7 +29,7 @@
 # Strips out blank lines and all comments except for "!DEF:", "!REF:", "!$acc" and "!$omp"
 with open(src, "r") as text_in:
     for line in text_in:
-        text = re.sub(r"!(?![DR]EF:|\$omp|\$acc).*", "", line, re.I)
+        text = re.sub(r"!(?![DR]EF:|\$omp|\$acc).*", "", line, flags=re.I)
         text = re.sub(r"^\s*$", "", text)
         diff1 += text