Add src/... to test_rules_scala, fix Windows break - #1724

Adds `src/...` to the `bazel build` and `bazel test` commands in
`test_rules_scala.sh` to follow up on bazel-contrib#1719 and bazel-contrib#1721.

Also includes:

- Adding `--test_output=errors` to each `bazel test` invocation to make
  failure messages visible in the CI logs.

- Joining the `contents` lines in
  `WorkerTest.testPersistentWorkerArgsfile` using the `line.separator`
  system property to fix a test failure on Windows.

- Swapping the arguments of `assertEquals()` assertions to `expected,
  actual` instead of `actual, expected` to fit the assertion failure
  messages.

---

After adding `src/...` to the `bazel test` commands in
`test_rules_scala.sh` the first time, the Windows build failed with:

- https://buildkite.com/bazel/rules-scala-scala/builds/5511#0195e775-498c-4ae5-b308-34cc70da65c4/75-257

```txt
//src/java/io/bazel/rulesscala/worker:worker_test  FAILED in 1.1s
  C:/.../testlogs/src/java/io/bazel/rulesscala/worker/worker_test/test.log

Executed 120 out of 120 tests: 119 tests pass and 1 fails locally.
 Test "bazel test src/... test/..." failed  (18 sec)

Traceback (most recent call last):
  File "c:\b\bk-windows-gd7g\bazel\rules-scala-scala\bazelci.py",
    line 4528, in <module>
      sys.exit(main())
               ^^^^^^
  File "c:\b\bk-windows-gd7g\bazel\rules-scala-scala\bazelci.py",
    line 4496, in main
      execute_commands(
  File "c:\b\bk-windows-gd7g\bazel\rules-scala-scala\bazelci.py",
    line 1232, in execute_commands
      PrepareRepoInCwd(True, initial_setup=True)
  File "c:\b\bk-windows-gd7g\bazel\rules-scala-scala\bazelci.py",
    line 1228, in PrepareRepoInCwd
      execute_batch_commands(task_config.get("batch_commands", None), print_cmd_groups)
  File "c:\b\bk-windows-gd7g\bazel\rules-scala-scala\bazelci.py",
    line 1741, in execute_batch_commands
      return subprocess.run(batch_commands, shell=True, check=True, env=os.environ).returncode
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\python3\Lib\subprocess.py",
    line 571, in run
      raise CalledProcessError(retcode, process.args,

subprocess.CalledProcessError:
  Command 'set PATH=/usr/bin;%PATH%&bash -lc "pacman --noconfirm --needed -S libxml2"&bash test_rules_scala.sh'
  returned non-zero exit status 3
```

Updating the `bazel test` command to add `--test_output=errors` made the
actual failure visible:

- https://buildkite.com/bazel/rules-scala-scala/builds/5513#0195e78b-6abc-42ea-95ee-8ddce41a64fb

```txt
FAIL: //src/java/io/bazel/rulesscala/worker:worker_test
  (see C:/.../testlogs/src/java/io/bazel/rulesscala/worker/worker_test/test.log)

INFO: From Testing //src/java/io/bazel/rulesscala/worker:worker_test:
===== Test output for //src/java/io/bazel/rulesscala/worker:worker_test:
JUnit4 Test Runner
...E
Time: 0.432
There was 1 failure:
1) testPersistentWorkerArgsfile(io.bazel.rulesscala.worker.WorkerTest)
org.junit.ComparisonFailure: expected:<line 1[
--flag_1
]ome arg
> but was:<line 1[
--flag_1
some arg]
>
  at org.junit.Assert.assertEquals(Assert.java:117)
  at org.junit.Assert.assertEquals(Assert.java:146)
  at io.bazel.rulesscala.worker.WorkerTest.testPersistentWorkerArgsfile(WorkerTest.java:73)
FAILURES!!!
Tests run: 3,  Failures: 1
```

This was due to the `line.separator` system property being `\r\n` on
Windows, and `\n` on every other platform. Notice the `]ome arg` line,
and the fact that this appeared as the `expected:` value in the
assertion failure message.