fix: use POSIX ERE [0-9] instead of \d in grep patterns for version discovery (#168)

The "Discover all versions" step in `publish-documentation.yml` used
`\d` in grep ERE patterns, which is not supported in POSIX ERE on Ubuntu
24.04. This caused `grep` to return exit code 1 (no matches), failing
the step under `pipefail`.

## Change
- Replace `\d` with `[0-9]` in both grep patterns in the `Discover all
versions` step:

```diff
- versions=$(ls api-reference/ | grep -E '^\d+\.\d+$' | sort -V | paste -sd ',' -)
- latest=$(ls api-reference/ | grep -E '^\d+\.\d+$' | sort -V | tail -1)
+ versions=$(ls api-reference/ | grep -E '^[0-9]+\.[0-9]+$' | sort -V | paste -sd ',' -)
+ latest=$(ls api-reference/ | grep -E '^[0-9]+\.[0-9]+$' | sort -V | tail -1)
```

`\d` requires `grep -P` (PCRE); POSIX ERE (`-E`) only recognises
`[0-9]`.

Author: Copilot

.github/workflows/publish-documentation.yml

@@ -100,8 +100,8 @@ jobs:
         id: discover-versions
         shell: bash
         run: |
-          versions=$(ls api-reference/ | grep -E '^\d+\.\d+$' | sort -V | paste -sd ',' -)
-          latest=$(ls api-reference/ | grep -E '^\d+\.\d+$' | sort -V | tail -1)
+          versions=$(ls api-reference/ | grep -E '^[0-9]+\.[0-9]+$' | sort -V | paste -sd ',' -)
+          latest=$(ls api-reference/ | grep -E '^[0-9]+\.[0-9]+$' | sort -V | tail -1)
           echo "versions=$versions" >> $GITHUB_OUTPUT
           echo "latest=$latest" >> $GITHUB_OUTPUT