docs: fix incorrect OR operator syntax in test-filters documentation

[thomhurst]

Summary

The documentation showed an invalid OR operator syntax that causes errors with Microsoft.Testing.Platform's TreeNodeFilter.

Invalid syntax (old):

(/*/*/Class1/*)|(/*/*/Class2/*)

This throws: A filter '/.*/.*/Class1/.*' should not contain a '/' character

Valid syntax (new):

/*/*/(Class1)|(Class2)/*

Root Cause

Microsoft.Testing.Platform's TreeNodeFilter validates that expressions being combined with operators (|, &) cannot contain the / path separator character. OR operations must occur within a single path segment, not across full paths.

From the TreeNodeFilter source:

case ValueExpression vExpr when vExpr.Value.Contains(PathSeparator):
    throw new ArgumentException(...);

Test plan

• Verify documentation renders correctly
• Test that the new example syntax works: dotnet run -- --treenode-filter "/*/*/(Class1)|(Class2)/*"

[thomhurst]

Summary

Fixes incorrect OR operator syntax in test-filters.md documentation that causes TreeNodeFilter validation errors.

Critical Issues

Incomplete Fix: This PR fixes one instance but leaves other incorrect examples in the codebase:

1. docs/docs/troubleshooting.md:1426 still shows:

   # Multiple filters (OR)
   dotnet run -- --treenode-filter "/*/*/ClassA/*|/*/*/ClassB/*"

   Should be: dotnet run -- --treenode-filter "/*/*/(ClassA)|(ClassB)/*"

2. docs/docs/troubleshooting.md:1621 still shows:

   # Run tests that are Integration OR Unit
   dotnet run -- --treenode-filter "/*/*/*/*[Category=Integration]|/*/*/*/*[Category=Unit]"

   This has the same issue - OR-ing complete paths instead of within a segment. The correct syntax should apply here too.

3. .github/copilot-instructions.md:139 shows vague example:

   # Multiple patterns (OR logic)
   --treenode-filter "Pattern1|Pattern2"

   Should clarify the OR must be within a single path segment.

Note: .claude/docs/workflows.md:50 already correctly identifies the old syntax as "Wrong" ✅

These inconsistencies will confuse users who find the incorrect examples in other documentation files.

Suggestions

Consider expanding this PR to fix all instances of incorrect OR syntax across the documentation to prevent confusion.

Verdict

⚠️ REQUEST CHANGES - Incomplete fix leaves incorrect examples in other documentation files