[CI] Lint only .sh files in the shell formatting pass (#7715)

The changed-file matcher reused the `*.sh` glob as a regular expression,
where the leading `*` applies to the `(^|/)` group instead of the file
name. Every path ending in "sh" matched, so NSIS include files (.nsh) were
handed to shellcheck and failed the format leg.

Match the suffix explicitly and keep the glob for the find(1) branch.

Co-authored-by: Lukas Brübach <Bruebach.Lukas@bdosecurity.de>

format.sh

@@ -33,6 +33,7 @@ cmakefile="CMakeLists.txt"
 cmakedir="cmake/.*\\.cmake"
 cmakeinclude=("cmake/gtest-CMakeLists.txt.in")
 scripts="*.sh"
+scriptsrx="[^/]*\\.sh$"
 color="--"
 verbosity=0
 sep="----------"
@@ -254,7 +255,7 @@ if [[ $branch ]]; then
   if [[ $do_shell ]]; then
     shell_names=()
     for name in "${basenames[@]}"; do
-      filerx="(^|/)$scripts$"
+      filerx="(^|/)$scriptsrx"
       if [[ $name =~ $filerx ]]; then
         shell_names+=("$name")
       fi