Disables the injectable pipe migration until we can decide whether this is the right solution for Ivy. Rolling it out properly will involve a more detailed plan and more changes like updating the styleguide, scaffolding schematics etc.
Context for the new `test-migrations.json`: since we use the `migrations.json` both for the real migrations and for tests, it doesn't allow us to disable a schematic, but continue running its tests. This change adds the test-specific file so that we can continue running the `injectable-pipe` tests, even though the schematic itself is disabled.
PR Close#30180
crisbeto