CI: Fix Nightly PyPi GitHub Action (#1683)

This was broken because we now import the version:
#1380 (comment)

The build has been broken for a while:
https://github.com/apache/iceberg-rust/actions/workflows/release_python_nightly.yml

Tested locally:

```
➜  iceberg-rust git:(fd-fix-version) ✗ export TIMESTAMP=123
CURRENT_VERSION=$(python3 -c "import toml; print(toml.load('bindings/python/Cargo.toml')['package']['version'])")
export NEW_VERSION="${CURRENT_VERSION}.dev${TIMESTAMP}"
➜  iceberg-rust git:(fd-fix-version) ✗ echo $NEW_VERSION
0.7.0.dev123
➜  iceberg-rust git:(fd-fix-version) ✗ python3 -c "
import toml
import os
config = toml.load('bindings/python/Cargo.toml')
new_version = os.environ['NEW_VERSION']
config['package']['version'] = new_version
with open('bindings/python/Cargo.toml', 'w') as f:
    toml.dump(config, f)
print(f'Updated version to: {new_version}')
"
Updated version to: 0.7.0.dev123
```

## Which issue does this PR close?

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- Closes #.

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Author: Fokko

.github/actions/overwrite-package-version/action.yml

@@ -38,14 +38,15 @@ runs:
       env:
         TIMESTAMP: ${{ inputs.timestamp }}
       run: |
-        CURRENT_VERSION=$(python -c "import toml; print(toml.load('bindings/python/pyproject.toml')['project']['version'])")
-        NEW_VERSION="${CURRENT_VERSION}.dev${TIMESTAMP}"
-        NEW_VERSION=$NEW_VERSION python -c "
+        CURRENT_VERSION=$(python -c "import toml; print(toml.load('bindings/python/Cargo.toml')['package']['version'])")
+        export NEW_VERSION="${CURRENT_VERSION}.dev${TIMESTAMP}"
+        python -c "
         import toml
         import os
-        config = toml.load('bindings/python/pyproject.toml')
-        config['project']['version'] = os.environ['NEW_VERSION']
-        with open('bindings/python/pyproject.toml', 'w') as f:
+        config = toml.load('bindings/python/Cargo.toml')
+        new_version = os.environ['NEW_VERSION']
+        config['package']['version'] = new_version
+        with open('bindings/python/Cargo.toml', 'w') as f:
             toml.dump(config, f)
-        print(f'Updated version to: {config[\"project\"][\"version\"]}')
+        print(f'Updated version to: {new_version}')
         "