docs(codepipeline): add note about repoString param resolvability at …

…runtime (#27109)

This PR addresses an issue encountered when setting up an AWS CDK pipeline where unresolved token values for the `repoString` parameter led to a runtime error. The updated docstring now explicitly mentions that the `repoString` must be resolvable at runtime and that unresolved tokens are intended to be a runtime error

Closes #27100.

Thanks to @peterwoodworth for the quick assessment and the proposed solution to the problem.

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/aws-cdk-lib/pipelines/lib/codepipeline/codepipeline-source.ts

@@ -101,7 +101,7 @@ export abstract class CodePipelineSource extends Step implements ICodePipelineAc
    * If you need access to symlinks or the repository history, be sure to set
    * `codeBuildCloneOutput`.
    *
-   * @param repoString A string that encodes owner and repository separated by a slash (e.g. 'owner/repo').
+   * @param repoString A string that encodes owner and repository separated by a slash (e.g. 'owner/repo'). The provided string must be resolvable at runtime.
    * @param branch The branch to use.
    * @param props The source properties, including the connection ARN.
    *