Make mcpb package version optional and fix schema validation (#686)

<!-- Provide a brief summary of your changes -->

## Motivation and Context
<!-- Why is this change needed? What problem does it solve? -->
The following PR:
* Makes mcpb package version property optional
* Bumps the schema and reflects that in the code
* Makes sure the publisher tests are being covered by doing `make check`

## How Has This Been Tested?
<!-- Have you tested this in a real application? Which scenarios were
tested? -->

## Breaking Changes
<!-- Will users need to update their code or configurations? -->

## Types of changes
<!-- What types of changes does your code introduce? Put an `x` in all
the boxes that apply: -->
- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] Documentation update

## Checklist
<!-- Go over all the following points, and put an `x` in all the boxes
that apply. -->
- [ ] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [ ] My code follows the repository's style guidelines
- [ ] New and existing tests pass locally
- [ ] I have added appropriate error handling
- [ ] I have added or updated documentation as needed

## Additional context
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-->

---------

Signed-off-by: Radoslav Dimitrov <radoslav@stacklok.com>

data/seed.json

@@ -1,6 +1,6 @@
 [
   {
-    "$schema": "https://static.modelcontextprotocol.io/schemas/2025-09-29/server.schema.json",
+    "$schema": "https://static.modelcontextprotocol.io/schemas/2025-10-17/server.schema.json",
     "name": "io.github.domdomegg/airtable-mcp-server",
     "description": "Read and write access to Airtable database schemas, tables, and records.",
     "repository": {
@@ -62,7 +62,7 @@
     ]
   },
   {
-    "$schema": "https://static.modelcontextprotocol.io/schemas/2025-09-29/server.schema.json",
+    "$schema": "https://static.modelcontextprotocol.io/schemas/2025-10-17/server.schema.json",
     "name": "io.github.domdomegg/airtable-mcp-server",
     "description": "Read and write access to Airtable database schemas, tables, and records.",
     "repository": {
@@ -115,7 +115,7 @@
     ]
   },
   {
-    "$schema": "https://static.modelcontextprotocol.io/schemas/2025-09-29/server.schema.json",
+    "$schema": "https://static.modelcontextprotocol.io/schemas/2025-10-17/server.schema.json",
     "name": "io.github.domdomegg/time-mcp-nuget",
     "description": "Get the current UTC time in RFC 3339 format.",
     "repository": {
@@ -136,7 +136,7 @@
     ]
   },
   {
-    "$schema": "https://static.modelcontextprotocol.io/schemas/2025-09-29/server.schema.json",
+    "$schema": "https://static.modelcontextprotocol.io/schemas/2025-10-17/server.schema.json",
     "name": "io.github.domdomegg/time-mcp-pypi",
     "description": "Get the current UTC time in RFC 3339 format.",
     "repository": {