explicitly specify gcc 11 hoping it will work

.github/workflows/gcc.yml

@@ -10,9 +10,9 @@ defaults:
 
 env:
   cache_key: gcc3  # The number (#) following the cache_key "gcc" is to flush Action cache.
-  CC: gcc-10
-  FC: gfortran-10
-  CXX: g++-10
+  CC: gcc-11
+  FC: gfortran-11
+  CXX: g++-11
 
 # A note on flushing Action cache and relevance to "cache_key" above.
 # There is no way to flush the Action cache, and hence a number (#) is appended