[1.6.x] Fixed #21035 -- Changed docs to treat the acronym SQL phonetically.

The documentation and comments now all use 'an' to
refer to the word SQL and not 'a'.

Backport of 4d13cc56de from master

tests/test_runner/tests.py

@@ -245,7 +245,7 @@ class Sqlite3InMemoryTestDbs(TestCase):
     available_apps = []
 
     @unittest.skipUnless(all(db.connections[conn].vendor == 'sqlite' for conn in db.connections),
-                         "This is a sqlite-specific issue")
+                         "This is an sqlite-specific issue")
     def test_transaction_support(self):
         """Ticket #16329: sqlite3 in-memory test databases"""
         old_db_connections = db.connections