[#1981] Change link to link to all first timer issues (#2233)

The link under 'Workflow' section of DG only links to frontend and
backend issues.

Let's link them to all types of first timer issues so that new 
contributors do not miss out on some other types of issues, such as 
DevOps.

docs/dg/workflow.md

@@ -26,7 +26,7 @@ Our workflow is mostly based on the guidelines given at se-education.org/guides.
 
 ## Find the suitable pull requests
 
-* If you are contributing to RepoSense for the first time, you can check the list of [backend issues](https://github.com/reposense/RepoSense/issues?q=is%3Aopen+is%3Aissue+label%3Aa-Backend+label%3Ad.FirstTimers) or [frontend issues](https://github.com/reposense/RepoSense/issues?q=is%3Aopen+is%3Aissue+label%3Ad.FirstTimers+label%3Aa-FrontEnd) for first timers.
+* If you are contributing to RepoSense for the first time, you can check the list of [issues that are suitable for first timers](https://github.com/reposense/RepoSense/issues?q=is%3Aopen+is%3Aissue+label%3Ad.FirstTimers).
 
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