docs: use 'go build .' in getting-started tutorials

'go build ./...' matches both the main package and the generated
package, and Go discards the resulting binaries when building more
than one package, so the tutorial step produced no executable.
Building the single main package with 'go build .' writes the binary
as the tutorials intend.

Fixes #4554

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FdtZb2F2AHRqAypxKhbTHn

Author: claude

docs/tutorials/getting-started-mysql.md

@@ -169,7 +169,7 @@ Before this code will compile you'll need to fetch the relevant MySQL driver:
 
 ```shell
 go get github.com/go-sql-driver/mysql
-go build ./...
+go build .
 ```
 
 The program should compile without errors. To make that possible, sqlc generates

docs/tutorials/getting-started-postgresql.md

@@ -188,7 +188,7 @@ package, but in this tutorial we've used `pgx/v5`:
 
 ```shell
 go get github.com/jackc/pgx/v5
-go build ./...
+go build .
 ```
 
 The program should compile without errors. To make that possible, sqlc generates

docs/tutorials/getting-started-sqlite.md

@@ -190,7 +190,7 @@ Before this code will compile you'll need to fetch the relevant SQLite driver:
 
 ```shell
 go get modernc.org/sqlite
-go build ./...
+go build .
 ```
 
 The program should compile without errors, and run successfully. To make that