Specify default permissions for `pr-instructions.yml` and `wr-pr-instructions.yml`

### Prerequisites
1. Be a member of Hack for LA. (There are no fees to join.) If you have not joined yet, please follow the steps on our [Getting Started](https://www.hackforla.org/getting-started) page and attend an onboarding session.
2. You have already read our [How to Contribute to Hack for LA Guide](https://github.com/hackforla/website/blob/gh-pages/CONTRIBUTING.md).
---
### Overview
We need to update the default permissions for the GitHub workflow specified in pr-instructions.yml and wr-pr-instructions.yml, so that it does not have more permissions than it needs.

### Details
To align with GitHub security best practices, we want to specify the minimum required permissions for each workflow via a top-level `permissions:` block to ensure that workflows only have the access they need by default.

Every GitHub Actions workflow automatically receives a `GITHUB_TOKEN` with a set of default repository permissions defined in the repo settings which may result in the workflow having more permissions than it needs to complete its job. By explicitly defining minimum default permissions at the workflow level, we can ensure that workflow has only the permissions it needs. Then if a job or step requires more access, those permissions can be explicitly granted using job-level permissions statements or step-level tokens (PATs).

We performed an audit to identify the minimum top-level permissions required for each workflow. The goal of this and related issues is to verify that each workflow continues to function correctly with the explicitly defined permissions. This approach helps minimize unnecessary privileges and strengthen overall repository security.

For additional info, see issue #8178 and [GitHub's recommendation for security best practice](https://docs.github.com/en/actions/security-for-github-actions/security-guides/automatic-token-authentication#modifying-the-permissions-for-the-github_token).

### Action Items
Note that this issue involves testing GitHub Actions. See "Resources/Instructions" below for how to set up your personal environment for testing.

Refer to [pr-instructions.yml](https://github.com/hackforla/website/blob/gh-pages/.github/workflow/pr-instructions.yml):
- [ ] Review the file to understand how the workflow is triggered. This is specified near the top of the YML in the `on:` section.
- [ ] Near the top of the file immediately **_before_** the line `jobs:` insert:
```
permissions:
contents: read
pull-requests: read
```
- [ ] Use clean formatting: make sure there is one line separation above and one below the permissions block.

Next, refer to [wr-pr-instructions.yml](https://github.com/hackforla/website/blob/gh-pages/.github/workflow/wr-pr-instructions.yml):
- [ ] Review the file to understand how the workflow is triggered. This is specified near the top of the YML in the `on:` section.
- [ ] Near the top of the file immediately **_before_** the line `jobs:` insert:
```
permissions:
contents: read
actions: read
issues: write
```
- [ ] Use clean formatting: make sure there is one line separation above and one below the permissions block.
- [ ] If the workflows include line(s) similar to the following, you will need to change these to match your situation before the workflow will run correctly:
```
if: github.repository == 'hackforla/website'
```
or
```
branches:
- 'gh-pages'
```
- [ ] Trigger the workflow to confirm whether both run successfully with no further changes to the permissions. Note that the second workflow is triggered by completion of the first.
- [ ] If there are errors:
- [ ] Try to determine the nature of the error, and whether it is occurring due to a mismatched repo or branch name.
- [ ] If you cannot track down the error, consult with the team via Slack or the weekly meetings to report your findings and get additional direction.
- [ ] If there are no errors, submit the PR like usual. Include a link to your test log.

### Resources/Instructions
- Refer to https://github.com/hackforla/website/issues/6537#issuecomment-2041147335, especially Tips 6, 7, and 8, if you have not already created you personal environment for testing.
- [How to Test GitHub Actions](https://drive.google.com/drive/u/0/folders/1MPY9CKcfKKN7hpDCG46ARrRzRSM8d8OA)
- [Additional Notes for GitHub Actions](https://docs.google.com/document/d/1frtvr5twBa_3yRGCG0divhlOMW8dPJxT/edit)
- [Tokens, Secrets, Scopes, & Permissions](https://github.com/hackforla/website/issues/8178#issuecomment-3314503242)