We already have "libnm-core/tests/test-keyfile.c" from which we build
"test-keyfile".

Our test binaries should be named the following:

- "*/tests/test-*"

- the test binary "*/tests/test-*" should be build from a source file
  "*/tests/test-*.c". Meaning: the source's and executable's name should
  correspond.

- test binaries should be named uniquely. Also, because older meson
  versions don't like having the same binary name more than once.

Rename to avoid the duplicate name.