doc: fix links

Fix link to the issue templates.

Signed-off-by: Alexandre Rey <alx.rey@icloud.com>

doc/contribute/external.rst

@@ -173,7 +173,7 @@ Follow the steps below to begin the submission process:
    detail, so that you are informed of the criteria used by the TSC and board in
    order to approve or reject a request
 #. Use the :github:`New External Source Code Issue
-   <new?assignees=&labels=RFC&template=007_ext-source.md&title=>` to open an issue
+   <new?assignees=&labels=RFC&template=007_ext-source.yml>` to open an issue
 #. Fill out all required sections, making sure you provide enough detail for the
    TSC to assess the merit of the request. Optionally you can also create a Pull
    Request that demonstrates the integration of the external source code and

doc/contribute/guidelines.rst

@@ -924,7 +924,7 @@ Requirements for Treewide Changes
   pull requests that are treewide changes
 
 - The person proposing a treewide change must create an `RFC issue
-  <https://github.com/zephyrproject-rtos/zephyr/issues/new?assignees=&labels=RFC&template=003_rfc-proposal.md&title=>`_
+  <https://github.com/zephyrproject-rtos/zephyr/issues/new?assignees=&labels=RFC&template=003_rfc-proposal.yml>`_
   describing the change, its rationale and impact, etc. before any pull
   requests related to the change can be merged
 

doc/project/project_roles.rst

@@ -63,7 +63,7 @@ level to the Zephyr GitHub repository.
 
 You may nominate yourself, or another GitHub user, for promotion to the Triage
 permission level by creating a GitHub issue, using the :github:`nomination
-template <new?assignees=&labels=Role+Nomination&template=006_nomination.md&title=>`.
+template <new?assignees=&labels=Role+Nomination&template=006_nomination.yml>`.
 
 Contributors granted the Triage permission level are permitted to add reviewers
 to a pull request and can be added as a reviewer by other GitHub users.