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/t1308-config-set.sh

@@ -166,14 +166,14 @@ test_expect_success 'find value with highest priority from a configset' '
 '
 
 test_expect_success 'find value_list for a key from a configset' '
-	cat >except <<-\EOF &&
+	cat >expect <<-\EOF &&
+	lama
+	ball
 	sam
 	bat
 	hask
-	lama
-	ball
 	EOF
-	test-tool config configset_get_value case.baz config2 .git/config >actual &&
+	test-tool config configset_get_value_multi case.baz config2 .git/config >actual &&
 	test_cmp expect actual
 '
 
@@ -238,8 +238,8 @@ test_expect_success 'error on modifying repo config without repo' '
 
 cmdline_config="'foo.bar=from-cmdline'"
 test_expect_success 'iteration shows correct origins' '
-	echo "[foo]bar = from-repo" >.git/config &&
-	echo "[foo]bar = from-home" >.gitconfig &&
+	printf "[ignore]\n\tthis = please\n[foo]bar = from-repo\n" >.git/config &&
+	printf "[foo]\n\tbar = from-home\n" >.gitconfig &&
 	if test_have_prereq MINGW
 	then
 		# Use Windows path (i.e. *not* $HOME)
@@ -253,19 +253,29 @@ test_expect_success 'iteration shows correct origins' '
 	value=from-home
 	origin=file
 	name=$HOME_GITCONFIG
+	lno=2
 	scope=global
 
+	key=ignore.this
+	value=please
+	origin=file
+	name=.git/config
+	lno=2
+	scope=local
+
 	key=foo.bar
 	value=from-repo
 	origin=file
 	name=.git/config
-	scope=repo
+	lno=3
+	scope=local
 
 	key=foo.bar
 	value=from-cmdline
 	origin=command line
 	name=
-	scope=cmdline
+	lno=-1
+	scope=command
 	EOF
 	GIT_CONFIG_PARAMETERS=$cmdline_config test-tool config iterate >actual &&
 	test_cmp expect actual