Fix memory leak in Parser::parse_media_query

[xzyfer]

e{@media_ #{}

Direct leak of 128 byte(s) in 1 object(s) allocated from:
--
  | #0 0x595afd in operator new(unsigned long) /src/llvm-project/compiler-rt/lib/asan/asan_new_delete.cpp:99:3
  | #1 0x87960a in Sass::Parser::parse_media_query() libsass/src/parser.cpp:2245:31
  | #2 0x7a6914 in Sass::Parser::parse_media_queries() libsass/src/parser.cpp:2225:56
  | #3 0x782dd4 in Sass::Parser::parseMediaRule() libsass/src/parser.cpp:2214:18
  | #4 0x74dcac in Sass::Parser::parse_block_node(bool) libsass/src/parser.cpp:264:55
  | #5 0x74290d in Sass::Parser::parse_block_nodes(bool) libsass/src/parser.cpp:171:11
  | #6 0x746b9a in Sass::Parser::parse_css_block(bool) libsass/src/parser.cpp:128:10
  | #7 0x7802e8 in parse_block libsass/src/parser.cpp:152:12
  | #8 0x7802e8 in Sass::Parser::parse_ruleset(Lookahead) libsass/src/parser.cpp:522:20
  | #9 0x74d26a in Sass::Parser::parse_block_node(bool) libsass/src/parser.cpp:260:21
  | #10 0x74290d in Sass::Parser::parse_block_nodes(bool) libsass/src/parser.cpp:171:11