Fix TEST_DOCS template: --suite takes directory not file

Passing a .test filepath to --suite causes MTR to error with
"Could not find ... in scanned directories". Test name must
be a positional argument, suite must be the directory.

AI=CLAUDE
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: villagesql-adam

villagesql/dev_server/TEST_DOCS.md.template

@@ -21,9 +21,10 @@ cd mysql-test
                     --veb-source-dir=/path/to/your/extension/build \
                     --parallel=auto
 
-# Run a specific test
-./mysql-test-run.pl --suite=/path/to/your/extension/tests/my_test.test \
-                    --veb-source-dir=/path/to/your/extension/build
+# Run a specific test (test name as positional argument)
+./mysql-test-run.pl --suite=/path/to/your/extension/tests \
+                    --veb-source-dir=/path/to/your/extension/build \
+                    my_test
 
 # Record test results (for creating .result files)
 ./mysql-test-run.pl --suite=/path/to/your/extension/tests \