Auxiliary: Modernize bash completion for ctest and cpack

This applies a similar modernization as was done in 1ff41ba26e
(Auxiliary: bash-completion: use _comp_initialize, 2024-06-02)
for the cmake executable. The _init_completion function was
deprecated upstream in bash-completion 2.12.

Auxiliary/bash-completion/cpack

@@ -3,7 +3,9 @@
 _cpack()
 {
     local cur prev words cword
-    if type -t _init_completion >/dev/null; then
+    if type -t _comp_initialize >/dev/null; then
+        _comp_initialize -n = || return
+    elif type -t _init_completion >/dev/null; then
         _init_completion -n = || return
     else
         # manual initialization for older bash completion versions

Auxiliary/bash-completion/ctest

@@ -3,7 +3,9 @@
 _ctest()
 {
     local cur prev words cword
-    if type -t _init_completion >/dev/null; then
+    if type -t _comp_initialize >/dev/null; then
+        _comp_initialize -n = || return
+    elif type -t _init_completion >/dev/null; then
         _init_completion -n = || return
     else
         # manual initialization for older bash completion versions