Modify tests to work with new '# flag' directive

The `# options: ...` directive was replaced with the `# flag: ...`
directive.

Author: MichaelLeeDBX

test-data/unit/check-incremental.test

@@ -1129,7 +1129,7 @@ tmp/m1.py:3: error: Argument 1 to "accepts_int" has incompatible type "str"; exp
 
 [case testIncrementalSilentImportsWithInnerImports]
 # cmd: mypy -m main foo
-# options: silent_imports
+# flags: --silent-imports
 
 [file main.py]
 from foo import MyClass
@@ -1154,7 +1154,7 @@ tmp/main.py:3: error: Revealed type is 'Any'
 [case testIncrementalSilentImportsWithInnerImportsAndNewFile]
 # cmd: mypy -m main foo
 # cmd2: mypy -m main foo unrelated
-# options: silent_imports
+# flags: --silent-imports
 
 [file main.py]
 from foo import MyClass