[backport/v1.9] Fix reading git notes from nested trees (#8189)

* Fix reading notes from nested trees

The GIT documentation for notes states "Permitted pathnames have the
form ab/cd/ef/.../abcdef...: a sequence of directory names of two
hexadecimal digits each followed by a filename with the rest of
the object ID."

* Add test case

* Fix new lines

modules/git/tests/repos/repo3_notes/objects/3e/668dbfac39cbc80a9ff9c61eb565d944453ba4

@@ -0,0 +1,3 @@
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modules/git/tests/repos/repo3_notes/objects/65/4c8b6b63c08bf37f638d3f521626b7fbbd4d37

@@ -0,0 +1 @@
+x
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