merge(third_party/git): Merge squashed git subtree at v2.23.0

Merge commit '1b593e1ea4' as 'third_party/git'

third_party/git/Documentation/RelNotes/1.7.0.1.txt

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+Git v1.7.0.1 Release Notes
+==========================
+
+Fixes since v1.7.0
+------------------
+
+ * In a freshly created repository "rev-parse HEAD^0" complained that
+   it is dangling symref, even though "rev-parse HEAD" didn't.
+
+ * "git show :no-such-name" tried to access the index without bounds
+   check, leading to a potential segfault.
+
+ * Message from "git cherry-pick" was harder to read and use than necessary
+   when it stopped due to conflicting changes.
+
+ * We referred to ".git/refs/" throughout the documentation when we
+   meant to talk about abstract notion of "ref namespace".  Because
+   people's repositories often have packed refs these days, this was
+   confusing.
+
+ * "git diff --output=/path/that/cannot/be/written" did not correctly
+   error out.
+
+ * "git grep -e -pattern-that-begin-with-dash paths..." could not be
+   spelled as "git grep -- -pattern-that-begin-with-dash paths..." which
+   would be a GNU way to use "--" as "end of options".
+
+ * "git grep" compiled with threading support tried to access an
+   uninitialized mutex on boxes with a single CPU.
+
+ * "git stash pop -q --index" failed because the unnecessary --index
+   option was propagated to "git stash drop" that is internally run at the
+   end.
+
+And other minor fixes and documentation updates.