Conform to pipeline-tasks tf-apply required input name

Changes proposed in this pull request:

In a2fb6357, I forgot that our own terraform-apply step calls a step by the same name in pipeline-tasks, and that step requires an input named terraform-templates. This change renames src to match, but keeps the same underlying resource, so the fix from a2fb6357 still applies.

Things to check

• For any logging statements, is there any chance that they could be logging sensitive data?
• Are log statements using a logging library with a logging level set? Setting a logging level means that log statements "below" that level will not be written to the output. For example, if the logging level is set to INFO and debugging statements are written with log.debug or similar, then they won't be written to the otput, which can prevent unintentional leaks of sensitive data.

Security considerations

None.