chore: convert changelog to markdown

.github/labeler.yml

@@ -2,7 +2,7 @@ docs:
   all:
     - changed-files:
       - all-globs-to-all-files:
-        - '!docs/changelog.rst'
+        - '!docs/changelog.md'
         - '!docs/upgrade.rst'
     - base-branch: "^(?!dependabot).*"
     - base-branch: "^(?!pre-commit-ci).*"

.github/labeler_merged.yml

@@ -3,6 +3,6 @@
 needs changelog:
   - all:
       - changed-files:
-          - all-globs-to-all-files: "!docs/changelog.rst"
+          - all-globs-to-all-files: "!docs/changelog.md"
       - base-branch: "^(?!dependabot).*"
       - base-branch: "^(?!pre-commit-ci).*"

.github/pull_request_template.md

@@ -9,11 +9,7 @@ It is recommended to use conventional commit format, see conventionalcommits.org
 
 ## Suggested changelog entry:
 
-<!-- Fill in the below block with the expected RestructuredText entry. Delete if no entry needed;
-     but do not delete header or rst block if an entry is needed! Will be collected via a script. -->
+<!-- Fill in the block below with the expected entry. Delete if no entry needed;
+     but do not delete the header if an entry is needed! Will be collected via a script. -->
 
-```rst
-
-```
-
-<!-- If the upgrade guide needs updating, note that here too -->
+* Placeholder.