fix: $$ not considered a variable

fixes:
Session variable '$GENERATES' does not exist

fakesnow/variables.py

@@ -49,8 +49,7 @@ def inline_variables(self, sql: str) -> str:
         for name, value in self._variables.items():
             sql = re.sub(rf"\${name}", value, sql, flags=re.IGNORECASE)
 
-        remaining_variables = re.search(r"\$\w+", sql)
-        if remaining_variables:
+        if remaining_variables := re.search(r"(?<!\$)\$\w+", sql):
             raise snowflake.connector.errors.ProgrammingError(
                 msg=f"Session variable '{remaining_variables.group().upper()}' does not exist"
             )

tests/test_fakes.py

@@ -1229,6 +1229,12 @@ def test_sfqid(cur: snowflake.connector.cursor.SnowflakeCursor):
     assert cur.sfqid == "fakesnow"
 
 
+def test_string_constant(cur: snowflake.connector.cursor.SnowflakeCursor):
+    assert cur.execute("""
+        select $$hello
+world$$""").fetchall() == [("hello\nworld",)]
+
+
 def test_tags_noop(cur: snowflake.connector.cursor.SnowflakeCursor):
     cur.execute("CREATE TABLE table1 (id int)")
     cur.execute("ALTER TABLE table1 SET TAG foo='bar'")