[bzlmod] first pin operation produces file with wrong name

Related to the lack of documentation for using this repo with bzlmod, I'm trying to write this up and running into some issues:

With this repro:

`MODULE.bazel`
```
bazel_dep(name = "rules_jvm_external", version = "4.5")
maven = use_extension("@rules_jvm_external//:extensions.bzl", "maven")

maven.install(
artifacts = ["org.seleniumhq.selenium:selenium-java:4.4.0"],
)

use_repo(maven, "maven")
```

then `bazel run @maven//:pin` and it creates a file named `rules_jvm_external~4.5~maven~maven_install.json`

I think this was meant to be just `maven_install.json`

Start with the MODULE.bazel reproduction and run `bazel run @maven//:pin` using the listed rules_jvm_external 4.5 setup. Compare the generated `rules_jvm_external~4.5~maven~maven_install.json` with the expected `maven_install.json`; done means the first pin operation creates the correctly named file.

Written by the indexing model from the issue text.