bug(go): Build fails due to type errors in pullrequests.go

## Bug Description
The server fails to build from source due to Go compiler errors. The errors indicate a non-boolean condition in an `if` statement and type mismatches when concatenating a string pointer with a string literal in the `pkg/github/pullrequests.go` file.

## Steps to Reproduce
1. Run the setup script: `bash setup-github-mcp.sh`

## Expected vs Actual Behavior
**Expected:** The script should successfully compile the Go source code and finish without errors.
**Actual:** The script fails with compiler errors.

## Environment
- **Go Version**: go1.22.2 linux/amd64
- **OS**: Linux

## Additional Context
```
# github.com/github/github-mcp-server/pkg/github
../../pkg/github/pullrequests.go:507:7: non-boolean condition in if statement
../../pkg/github/pullrequests.go:523:9: invalid operation: result.Message += fmt.Sprintf("...") (mismatched types *string and string)
../../pkg/github/pullrequests.go:529:9: invalid operation: result.Message += fmt.Sprintf("...") (mismatched types *string and string)
Error: Failed to build GitHub MCP server
```

## Possible Solution
The `result.Message` variable is a pointer (`*string`) and needs to be dereferenced before string concatenation (e.g., `*result.Message += ...`). The `if` statement on line 507 requires an explicit boolean condition.

Start with bash setup-github-mcp.sh and inspect pkg/github/pullrequests.go around lines 507, 523, and 529, using the reported Go compiler errors as the guide. Rebuild through the setup script and confirm the GitHub MCP server compiles without the listed type errors.

Written by the indexing model from the issue text.