Stop subprocesses from using inherited or default PAGER

At startup, set PAGER to "cat" so that any inherited or
default value of PAGER does not affect subprocesses of
Emacs.  Pagers generally won't work when a subprocess
runs under Emacs.
Users can use 'comint-pager' (or other customizations)
to tell subprocesses to use a different specific pager.
* lisp/startup.el (normal-top-level): Set PAGER to 'cat',
if 'cat' is available.  (Bug#72426)

lisp/startup.el

@@ -854,6 +854,12 @@ It is the default value of the variable `top-level'."
     ;; We are careful to do it late (after term-setup-hook), although the
     ;; new multi-tty code does not use $TERM any more there anyway.
     (setenv "TERM" "dumb")
+    ;; Similarly, a subprocess should not try to invoke a pager, as most
+    ;; pagers will fail in a dumb terminal.  Many programs default to
+    ;; using "less" when PAGER is unset, so set PAGER to "cat"; using cat
+    ;; as a pager is equivalent to not using a pager at all.
+    (when (executable-find "cat")
+      (setenv "PAGER" "cat"))
     ;; Remove DISPLAY from the process-environment as well.  This allows
     ;; `callproc.c' to give it a useful adaptive default which is either
     ;; the value of the `display' frame-parameter or the DISPLAY value