libstdc++: Fix typos in comments in tests

libstdc++-v3/ChangeLog:

	* testsuite/20_util/optional/monadic/and_then.cc: Fix typo.
	* testsuite/20_util/optional/monadic/transform.cc: Likewise.
	* testsuite/22_locale/codecvt/always_noconv/char/1.cc: Likewise.
	* testsuite/22_locale/codecvt/encoding/char/1.cc: Likewise.
	* testsuite/22_locale/codecvt/in/char/1.cc: Likewise.
	* testsuite/22_locale/codecvt/max_length/char/1.cc: Likewise.
	* testsuite/22_locale/codecvt/out/char/1.cc: Likewise.
	* testsuite/22_locale/codecvt/unshift/char/1.cc: Likewise.