ct: fix -dir and ERL_LIBS for app-provider compiled_suites

[sebastiw]

Two regressions in private/ct.bzl::_impl, both surfacing only when an ErlangAppInfo-providing target (e.g. a :test_erlang_app produced by extract_app(test = True)) is passed as compiled_suites rather than the bare erlang_bytecode outputs the ct_suite macro produces.

1. -dir test is bogus when the suite beam is not in test/

8faae61 ("Resurrect CI: ... -dir ebin -> -dir test") fixed the ct_suite macro path (its erlang_bytecode("..._beam_files", dest = "test") puts the suite at test/<suite>.beam) but hardcoded the arg. When compiled_suites is an extract_app target, the suite beam post-e70ed5a lives at <target>/ebin/<suite>.beam — no test/ exists in the runfiles tree. ct_run aborts with

Directory .../test is invalid
Test run failed! Reason: {make_failed, [...]}

Compute -dir from the package-relative dirnames of the _SUITE.beam entries in compiled_suites; fall back to "test" when none are found (defensive — ct_run would error on an empty -dir arg). Drop the now-redundant -pa <dir> for any path already covered by -dir.

2. ERL_LIBS missing the app under test and its prod deps

228b062 originally built ERL_LIBS via
flat_deps(ctx.attr.deps + ctx.attr.compiled_suites). 8faae61 narrowed that to flat_deps(ctx.attr.deps) because compiled_suites under the ct_suite macro are erlang_bytecode outputs and don't provide ErlangAppInfo, so flat_deps's dep[ErlangAppInfo] access fails at analysis.

That's correct for the macro path, but it stripped the transitive app closure that an extract_app(test = True) target contributes. Suites that rely on application:ensure_all_started/1 of the app under test then fail init_per_suite because the app's prod deps are not in ERL_LIBS, e.g.

{badmatch,{error,{some_dep,{"no such file or directory" ...

Re-include only the ErlangAppInfo-providing entries of compiled_suites in the flat_deps call, leaving plain .beam targets alone.

Validation

• cd test && bazelisk test //... -> 13/13 PASS
• cd examples/umbrella && bazelisk test //... -> 9/9 PASS
  (covers the ct_suite macro path via umbrella_smoke_SUITE).
• Reproduced and fixed against a downstream consumer with ct_test
  targets of the form
  ct_test(compiled_suites = [":test_erlang_app"], ...):
  before, every such target failed with the Directory ... is invalid
  error above (or, with Bump golang.org/x/net from 0.17.0 to 0.23.0 in /test #1 alone applied, init_per_suite crashed on
  the missing prod dep); after, they pass.