Enable code block evaluation when generating .org manuals

* doc/misc/Makefile.in ($(1:.org=.texi)): Enable code
block evaluation in Org mode manual and other .org manuals
to produce automatically generated parts.  (Bug#71394)
When testing a scratch sync to the Emacs repo, the build
failed with

 make[3]: Leaving directory '/home/kyle/src/savannah/emacs--master/lisp'
 Evaluate this emacs-lisp code block on your system? (yes or no)
 Error: end-of-file ("Error reading from stdin")
   yes-or-no-p("Evaluate this emacs-lisp code block on your system? ")

That's expected given 715148131 (org-manual: Automatically
generate export option list, 2023-07-31) and the default
org-confirm-babel-evaluate value.

doc/misc/Makefile.in

@@ -250,6 +250,7 @@ define org_template
  $(1:.org=.texi): $(1) ${top_srcdir}/lisp/org/ox-texinfo.el
 	$${AM_V_GEN}cd "$${srcdir}" && $${emacs} -l ox-texinfo \
 	  --eval '(setq gc-cons-threshold 50000000)' \
+	  --eval '(setq org-confirm-babel-evaluate nil)' \
 	  -f org-texinfo-export-to-texinfo-batch $$(notdir $$<) $$(notdir $$@)
 endef