Allow test_all.sh to pass under Bazel 7

`bash ./test_all.sh` passes after minor updates to the following test
cases to handle slightly different behavior under Bazel 7:

- `test_custom_reporter_class_has_been_set` makes the test output dir
  writable, since it no longer is by default.

- `test_scala_import_expect_failure_on_missing_direct_deps_warn_mode`
  removes preexisting output, since Bazel 7 won't emit warnings if it
  already exists.

---

FYI: Under Bazel 7.0 and Bazel 7.1, buildifier warnings for external
targets in the following test cases changed to begin with `@@repo_name`
instead of `@repo_name`:

- test/shell/test_scala_library.sh:
  `test_scala_library_expect_failure_on_missing_direct_external_deps_jar`
  `test_scala_library_expect_failure_on_missing_direct_external_deps_file_group`

- test/shell/test_strict_dependency.sh:
  `test_stamped_target_label_loading`
  `test_strict_deps_filter_included_target`

- test/shell/test_test_unused_dependency.sh:
  `test_unused_deps_filter_included_target`

However, as of Bazel 7.2, those warnings changed back to `@repo_name`,
so those changes aren't reflected in this commit.

test/shell/test_custom_reporter_class.sh

@@ -22,9 +22,10 @@ test_custom_reporter_class_has_been_set() {
   bazel test test/scala_test:custom_reporter
   set +e
   reporter_output_dir="$(bazel info bazel-testlogs)/test/scala_test/custom_reporter/test.outputs"
+  chmod u+w "$reporter_output_dir"  # Needed under Bazel 7
   reporter_output_filepath="${reporter_output_dir}/${custom_reporter_check_file}"
   unzip -oq "${reporter_output_dir}/outputs.zip" -d "${reporter_output_dir}"
   assert_file_exists "${reporter_output_filepath}"
 }
 
-$runner test_custom_reporter_class_has_been_set
+$runner test_custom_reporter_class_has_been_set

test/shell/test_strict_dependency.sh

@@ -21,6 +21,9 @@ test_scala_import_expect_failure_on_missing_direct_deps_warn_mode() {
   dependency_target2='//test_expect_failure/scala_import:guava'
   test_target='test_expect_failure/scala_import:scala_import_propagates_compile_deps'
 
+  # Bazel 7 won't emit warnings if the output already exists.
+  rm -f "$(bazel info bazel-bin)/${test_target/://}"*
+
   local expected_message1="buildozer 'add deps $dependency_target1' //$test_target"
   local expected_message2="buildozer 'add deps $dependency_target2' //$test_target"