Fix #5699: Update wiki deployment permissions (#5700)

## Explanation
Fixes #5699

This attempts to fix #5699 by updating the job permissions for wiki
deployment to include access to content writing (which is now off by
default at the Oppia organization level--see #5699). It's not clear
whether this will fix the issue since GitHub's documentation is unclear
as to which permissions are required in order to be able to push to the
wiki, but it seems likely that 'contents' is the correct permission per
https://docs.github.com/en/actions/writing-workflows/choosing-what-your-workflow-does/controlling-permissions-for-github_token#overview.
Unfortunately, the fix can't be verified until after the PR is merged as
the deployment job only runs manually or upon a PR merging.

Note that the permission is intentionally being set job-specific to
avoid over-subscribing permissions at the workflow level (since the
other job and potentially future jobs in this workflow do not need
content write access).

## Essential Checklist
- [x] The PR title and explanation each start with "Fix #bugnum: " (If
this PR fixes part of an issue, prefix the title with "Fix part of
#bugnum: ...".)
- [x] Any changes to
[scripts/assets](https://github.com/oppia/oppia-android/tree/develop/scripts/assets)
files have their rationale included in the PR explanation.
- [x] The PR follows the [style
guide](https://github.com/oppia/oppia-android/wiki/Coding-style-guide).
- [x] The PR does not contain any unnecessary code changes from Android
Studio
([reference](https://github.com/oppia/oppia-android/wiki/Guidance-on-submitting-a-PR#undo-unnecessary-changes)).
- [x] The PR is made from a branch that's **not** called "develop" and
is up-to-date with "develop".
- [x] The PR is **assigned** to the appropriate reviewers
([reference](https://github.com/oppia/oppia-android/wiki/Guidance-on-submitting-a-PR#clarification-regarding-assignees-and-reviewers-section)).

## For UI-specific PRs only
N/A -- this is an infrastructure-only change that also only affects wiki
deployment and verification workflows.

.github/workflows/wiki.yml

@@ -36,6 +36,8 @@ jobs:
           bazel run //scripts:wiki_table_of_contents_check -- ${GITHUB_WORKSPACE}
 
   wiki-deploy:
+    permissions:
+      contents: write
     runs-on: ${{ matrix.os }}
     strategy:
       matrix: