Prefer defface's ':slant italic' to obsolete alias ':italic t'

Prefer defface's ':slant italic' to obsolete alias ':italic t'

* etc/themes/manoj-dark-theme.el (manoj-dark):
* etc/themes/modus-themes.el (modus-themes-faces):
* etc/themes/manoj-dark-theme.el (manoj-dark):
* etc/themes/modus-themes.el (modus-themes-faces):
* lisp/emacs-lisp/eieio-custom.el (eieio-custom-slot-tag-face):
* lisp/gnus/gnus-art.el (gnus-emphasis-italic)
(gnus-emphasis-underline-italic, gnus-emphasis-bold-italic)
(gnus-emphasis-underline-bold-italic, gnus-signature)
(gnus-header-from, gnus-header-subject, gnus-header-newsgroups)
(gnus-header-content):
* lisp/gnus/gnus-cite.el (gnus-cite-attribution, gnus-cite-1)
(gnus-cite-2, gnus-cite-3, gnus-cite-4, gnus-cite-5, gnus-cite-6)
(gnus-cite-7, gnus-cite-8, gnus-cite-9, gnus-cite-10, gnus-cite-11):
* lisp/gnus/gnus-srvr.el (gnus-server-cloud-host)
(gnus-server-closed):
* lisp/gnus/gnus.el (gnus-group-mail-1-empty)
(gnus-group-mail-2-empty, gnus-summary-low-ticked)
(gnus-summary-low-ancient, gnus-summary-low-undownloaded)
(gnus-summary-low-unread, gnus-summary-low-read):
* lisp/gnus/message.el (message-header-to)
(message-header-newsgroups, message-header-other):
* lisp/gnus/mm-decode.el (mm-command-output):
* lisp/mh-e/mh-e.el (mh-face-data, mh-folder-body):
* lisp/net/dictionary.el (dictionary-word-entry-face):
* lisp/org/org-faces.el (org-formula, org-agenda-date-today)
(org-scheduled, org-scheduled-today):
* lisp/proced.el (proced-interruptible-sleep-status-code):
* lisp/progmodes/prolog.el (prolog-font-lock-keywords):
* lisp/progmodes/verilog-mode.el (verilog-font-lock-translate-off-face)
(verilog-font-lock-p1800-face, verilog-font-lock-ams-face)
(verilog-font-lock-grouping-keywords-face):
* lisp/progmodes/vhdl-mode.el (vhdl-font-lock-attribute-face)
(vhdl-font-lock-enumvalue-face, vhdl-font-lock-function-face)
(vhdl-font-lock-directive-face):
* lisp/transient.el (transient-inapt-suffix):
* lisp/vc/ediff-init.el (ediff-even-diff-A, ediff-even-diff-B)
(ediff-even-diff-C, ediff-even-diff-Ancestor, ediff-odd-diff-A)
(ediff-odd-diff-B, ediff-odd-diff-C, ediff-odd-diff-Ancestor):
Prefer defface attribute ':slant italic' to its obsolete alias
':italic t'.  See also Bug#73552.

(cherry picked from commit 64d314e0f6495de6fcf4f4c51e710b597a237e4f)