Auto merge of #23718 - asajeffrey:gitattributes-binary-files, r=jdm

Declare image files as binaries in gitignore

Explicitly declare image files to be binaries in .gitattributes, so as to avoid crlf-munging

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.gitattributes

@@ -1,2 +1,6 @@
 * text=auto eol=lf
 tests/* linguist-vendored
+
+# Denote all files that are truly binary and should not be modified.
+*.png binary
+*.jpg binary