test: fix format of dictionaries

According to libFuzzer documentation [1] backslash should be escaped.

1. https://llvm.org/docs/LibFuzzer.html#dictionaries

```
$ swim_proto_meta_fuzzer -dict=swim_proto_meta_fuzzer.dict
ParseDictionaryFile: error in line 1
                "\001\000\000\004"
$ swim_proto_member_fuzzer -dict=swim_proto_member_fuzzer.dict
ParseDictionaryFile: error in line 1
                "\022\000\000\000\000\000\000\000"
```

NO_CHANGELOG=internal
NO_DOC=internal
NO_TEST=internal

test/static/swim_proto_member_fuzzer.dict

-"\022\000\000\000\000\000\000\000"
-"\272\376\377\377\377\377\377\377"
+"\\022\\000\\000\\000\\000\\000\\000\\000"
+"\\272\\376\\377\\377\\377\\377\\377\\377"

test/static/swim_proto_meta_fuzzer.dict

-"\001\000\000\004"
-"\001\000"
+"\\001\\000\\000\\004"
+"\\001\\000"