merge(3p/git): Merge git subtree at v2.29.2

This also bumps the stable nixpkgs to 20.09 as of 2020-11-21, because
there is some breakage in the git build related to the netrc
credentials helper which someone has taken care of in nixpkgs.

The stable channel is not used for anything other than git, so this
should be fine.

Change-Id: I3575a19dab09e1e9556cf8231d717de9890484fb

third_party/git/t/t7417-submodule-path-url.sh

@@ -25,4 +25,21 @@ test_expect_success 'fsck rejects unprotected dash' '
 	grep gitmodulesPath err
 '
 
+test_expect_success MINGW 'submodule paths disallows trailing spaces' '
+	git init super &&
+	test_must_fail git -C super submodule add ../upstream "sub " &&
+
+	: add "sub", then rename "sub" to "sub ", the hard way &&
+	git -C super submodule add ../upstream sub &&
+	tree=$(git -C super write-tree) &&
+	git -C super ls-tree $tree >tree &&
+	sed "s/sub/sub /" <tree >tree.new &&
+	tree=$(git -C super mktree <tree.new) &&
+	commit=$(echo with space | git -C super commit-tree $tree) &&
+	git -C super update-ref refs/heads/master $commit &&
+
+	test_must_fail git clone --recurse-submodules super dst 2>err &&
+	test_i18ngrep "sub " err
+'
+
 test_done