ci: Ensure assignees can be set for generated PRs (#62418)

Now, this is one of these beautiful cases where GitHubs API ist just so
pleasant to work with: Because PRs are treated as issues, assigning an
assignee to a PR suddenly requires issue write permissions, despite the
issue in question being a PR. Not having that permission resulted in
some missing assignees on zed zippy bumps and failures of the workflows
as seen in
https://github.com/zed-industries/zed/actions/runs/31339736929/job/93311493258.

In comparison, labelling PRs requires PR write permissions as seen in
https://github.com/zed-industries/zed/pull/61525 🤡

Beautiful API and a pleasure to work with, 10/10 would recommend. 

Release Notes:

- N/A

.github/workflows/bump_zed_version.yml

@@ -104,6 +104,7 @@ jobs:
         owner: ${{ github.repository_owner }}
         repositories: ${{ github.event.repository.name }}
         permission-contents: write
+        permission-issues: write
         permission-pull-requests: write
     - name: steps::checkout_repo
       uses: actions/checkout@93cb6efe18208431cddfb8368fd83d5badbf9bfd

.github/workflows/extension_bump.yml

@@ -84,6 +84,7 @@ jobs:
         owner: ${{ github.repository_owner }}
         repositories: ${{ github.event.repository.name }}
         permission-contents: write
+        permission-issues: write
         permission-pull-requests: write
     - name: steps::checkout_repo
       uses: actions/checkout@93cb6efe18208431cddfb8368fd83d5badbf9bfd

.github/workflows/extension_workflow_rollout.yml

@@ -125,8 +125,9 @@ jobs:
         private-key: ${{ secrets.ZED_ZIPPY_APP_PRIVATE_KEY }}
         owner: zed-extensions
         repositories: ${{ matrix.repo }}
-        permission-pull-requests: write
         permission-contents: write
+        permission-issues: write
+        permission-pull-requests: write
         permission-workflows: write
     - name: checkout_extension_repo
       uses: actions/checkout@93cb6efe18208431cddfb8368fd83d5badbf9bfd

.github/workflows/publish_extension_cli.yml

@@ -72,6 +72,7 @@ jobs:
         owner: ${{ github.repository_owner }}
         repositories: ${{ github.event.repository.name }}
         permission-contents: write
+        permission-issues: write
         permission-pull-requests: write
         permission-workflows: write
     - name: steps::checkout_repo
@@ -129,6 +130,7 @@ jobs:
         owner: zed-industries
         repositories: extensions
         permission-contents: write
+        permission-issues: write
         permission-pull-requests: write
         permission-workflows: write
     - id: short-sha