Attempt to fix version_specifier in GHCR publish step (#1435)

The publish to GHCR step is currently failing with this error:

![image](https://github.com/user-attachments/assets/2bd96bee-3acd-49df-8ece-8a7d2920288a)

## Actual
The resulting command generated is `RUN pip install
cartography'==0.98.0rc3'`..

## Expected
.. when I wanted it to be `RUN pip install cartography==0.98.0rc3`.


## In this PR
I adjusted the version specifier and re-tested it locally and _think_
that this will now work in GitHub actions.


![image](https://github.com/user-attachments/assets/fe40c3bf-c12c-4a2b-94d3-78235850018b)

Signed-off-by: Alex Chantavy <[email protected]>

.github/workflows/publish-to-ghcr-and-pypi.yml

@@ -86,4 +86,4 @@ jobs:
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}
           # e.g. '==0.98.0'
-          build-args: VERSION_SPECIFIER='==${{ env.VERSION }}'
+          build-args: VERSION_SPECIFIER===${{ env.VERSION }}