Add CI check for mixed line endings

Trigger workflow on all file changes.

Closes https://github.com/wxWidgets/wxWidgets/pull/2224

misc/scripts/check_mixed_eol.sh

@@ -0,0 +1,35 @@
+#!/bin/bash
+
+cd `dirname "$0"`/../..
+
+find . \(                         \
+    -path './.git'      -prune -o \
+    -path './3rdparty'  -prune -o \
+    -path './src/expat' -prune -o \
+    -path './src/jpeg'  -prune -o \
+    -path './src/png'   -prune -o \
+    -path './src/tiff'  -prune -o \
+    -path './src/zlib'  -prune \) \
+    -o -type f -print0 |
+(
+while IFS= read -r -d '' file; do
+    case "$file" in
+    *.ani | *.bmp | *.chm | *.dia | *.gif | *.gz | *.hlp | *.icns | *.ico | *.jpg | *.mo | *.mpg | *.pcx | *.pdf | *.png | *.pnm | *.tga | *.tif | *.ttf | *.wav | *.zip )
+        continue
+        ;;
+    esac
+
+    read dos unix mac <<< $(dos2unix --info=dum "$file" | awk '{print $1, $2, $3}')
+    if [[ "$dos" -eq "0" ]] && [[ "$unix" -eq "0" ]]; then
+        :
+    elif [[ "$dos" -eq "0" ]] && [[ "$mac" -eq "0" ]]; then
+        :
+    elif [[ "$unix" -eq "0" ]] && [[ "$mac" -eq "0" ]]; then
+        :
+    else
+        echo "$file has mixed EOL"
+        rc=$((rc+1))
+    fi
+done
+exit $rc
+)