Separate out tasks for each merge in the Prepare Release script

So it's easier to see which one failed.

.github/workflows/release_prepare.yml

@@ -70,11 +70,30 @@ jobs:
                   fetch-tags: true
                   token: ${{ secrets.ELEMENT_BOT_TOKEN }}
 
-            - name: Merge develop
+            - name: Merge Element Desktop
+              if: inputs.element-desktop
               run: |
                   git config --global user.email "releases@riot.im"
                   git config --global user.name "RiotRobot"
-                  for REPO in $REPOS; do [ -d "$REPO" ] && git -C "$REPO" merge origin/develop; done
+                  git -C "element-desktop" merge origin/develop
+            - name: Merge Element Web
+              if: inputs.element-web
+              run: |
+                  git config --global user.email "releases@riot.im"
+                  git config --global user.name "RiotRobot"
+                  git -C "element-web" merge origin/develop
+            - name: Merge React SDK
+              if: inputs.matrix-react-sdk
+              run: |
+                  git config --global user.email "releases@riot.im"
+                  git config --global user.name "RiotRobot"
+                  git -C "matrix-react-sdk" merge origin/develop
+            - name: Merge JS SDK
+              if: inputs.matrix-js-sdk
+              run: |
+                  git config --global user.email "releases@riot.im"
+                  git config --global user.name "RiotRobot"
+                  git -C "matrix-js-sdk" merge origin/develop
 
             - name: Push staging
               run: for REPO in $REPOS; do [ -d "$REPO" ] && git -C "$REPO" push origin staging; done