cc_fuzztest_grammar_library bazel macro cannot be used outside of com_google_fuzztest repo

```py
# some/package/BUILD
load("@com_google_fuzztest//build_defs:cc_fuzztest_grammar_library.bzl", "cc_fuzztest_grammar_library")

cc_fuzztest_grammar_library(
name = "some_grammar",
srcs = ["some_grammar.g4"],
top_level_rule = "some_rule",
)
```
results in
```
ERROR: no such package 'fuzztest': BUILD file not found in any of the following directories. Add a BUILD file to a directory to mark it as a package.
- /path/to/my/workspace/fuzztest
ERROR: /path/to/my/workspace/some/package/BUILD:122:28: no such package 'fuzztest': BUILD file not found in any of the following directories. Add a BUILD file to a directory to mark it as a package.
- /path/to/my/workspace/fuzztest and referenced by '//some/package:some_grammar'
ERROR: Analysis of target '//some/package:some_grammar' failed; build aborted: Analysis failed
```

The linked PR fixes the issue.