Use lexical-binding in most remaining tests

Use lexical-binding in most remaining tests

* test/lisp/comint-tests.el:
* test/lisp/custom-resources/custom--test-theme.el:
* test/lisp/dabbrev-tests.el:
* test/lisp/emulation/viper-tests.el:
* test/lisp/erc/erc-track-tests.el:
* test/lisp/gnus/gnus-tests.el:
* test/lisp/imenu-tests.el:
* test/lisp/info-xref-tests.el:
* test/lisp/jit-lock-tests.el:
* test/lisp/json-tests.el:
* test/lisp/man-tests.el:
* test/lisp/replace-tests.el:
* test/lisp/shadowfile-tests.el:
* test/lisp/subr-tests.el:
* test/lisp/thingatpt-tests.el:
* test/lisp/xml-tests.el: Use lexical-binding.

* test/lisp/man-tests.el (man-tests-filter-strings):
* test/lisp/shadowfile-tests.el (shadow-test00-clusters)
(shadow-test01-sites, shadow-test06-literal-groups)
(shadow-test07-regexp-groups, shadow-test09-shadow-copy-files):
Silence byte-compiler.