Don't build test dependencies for manual tests

The `owners-ts-tests` target is only used for tests that
themselves are not automatically run. Running `bazelisk build //...`
would still build that target, which is unnecessary and would fail
because of unknown import of 'sinon'.

Change-Id: Iba13fa92003825678118df41d38638c080a7cad2

web/BUILD

diff --git a/web/BUILD b/web/BUILD
index 01b126f..e07c811 100644
--- a/web/BUILD
+++ b/web/BUILD
@@ -43,6 +43,7 @@
     incremental = True,
     out_dir = "_bazel_ts_out_tests",
     tsconfig = ":tsconfig",
+    tags = ["manual"],
     deps = [
         "//plugins:node_modules",
         "//polygerrit-ui:node_modules",