fix(ci): fix link-checker context and prevent deploy on PR

[ItsCurulo]

Summary :
This PR addresses issue #145 by updating the CI pipeline configuration to correctly handle Pull Requests.
Currently, the link checker defaults to the main branch or fails to trigger on PRs, leading to false positives/negatives. This fix ensures the workflow scans the actual code being proposed in the PR.

Changes

1. Modified Trigger: Added pull_request trigger to ci.yaml.
2. Fixed Checkout Context: Updated the link_checker job to use ref: ${{ github.event.pull_request.head.sha || github.sha }}. Ths targets the specific commit of the PR.
3. Safety Check: Added a conditional check (if: github.event_name == 'push' ...) to the deploy job. This prevents the pipeline from attempting to deploy the documentation website during a PR check.

Closes #145

Description for the changelog :
Fixed CI pipeline configuration to correctly handle Link Checker and deployments on Pull Requests.

Declaration:

• content meets the license for this project
• AI has not been used, or has been declared, in this pull request

Other info :
Tested in a forked repository. The workflow successfully triggered on the Pull Request and scanned the files as expected.

Output summary from the test run:

Run lycheeverse/lychee-action@v2.7.0
# Summary

| Status | Count |
|----------------|-------|
| 🔍 Total | 2638 |
| ✅ Successful | 1927 |
| ⏳ Timeouts | 0 |
| 🔀 Redirected | 6 |
| 👻 Excluded | 703 |
| ❓ Unknown | 0 |
| 🚫 Errors | 1 |
| ⛔ Unsupported | 1 |

[jgadsden]

Hello @ItsCurulo , can you confirm that no AI was used in this pull request? The wording of the pull request and the solution you have proposed have the 'feel' of AI

The solution does not implement a fix for issue #145 - the fix must be in the pull request pipepline

[jgadsden]

the fix needs to be in the pull request pipeline not the commit pipeline

[ItsCurulo]

Hello @jgadsden, thank you for the feedback.
Honestly, since this was my first contribution, I used an AI tool to help me format the pull request description more clearly.
I apologize for the confusion. I thought that ci.yaml handled both workflows, my fault.

[jgadsden]

no need for a change to double quotes here, as no escape sequences are expected, so can be reverted

[jgadsden]

same comment as for line 49

[jgadsden]

ne need for new line

[jgadsden]

as above, no need for double quotes as there are no escape sequences, same for line 86

[jgadsden]

this is implied by the pull request action and so is not needed

[jgadsden]

it would be good to implement this by excluding the 'blob' links that are actually causing the failures when .md files are added / deleted within a pull request
see lycheedocs for how to do this, along with the .lycheeignore file