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/t6501-freshen-objects.sh

@@ -128,33 +128,33 @@ for repack in '' true; do
 done
 
 test_expect_success 'do not complain about existing broken links (commit)' '
-	cat >broken-commit <<-\EOF &&
-	tree 0000000000000000000000000000000000000001
-	parent 0000000000000000000000000000000000000002
+	cat >broken-commit <<-EOF &&
+	tree $(test_oid 001)
+	parent $(test_oid 002)
 	author whatever <whatever@example.com> 1234 -0000
 	committer whatever <whatever@example.com> 1234 -0000
 
 	some message
 	EOF
 	commit=$(git hash-object -t commit -w broken-commit) &&
-	git gc 2>stderr &&
+	git gc -q 2>stderr &&
 	verbose git cat-file -e $commit &&
 	test_must_be_empty stderr
 '
 
 test_expect_success 'do not complain about existing broken links (tree)' '
-	cat >broken-tree <<-\EOF &&
-	100644 blob 0000000000000000000000000000000000000003	foo
+	cat >broken-tree <<-EOF &&
+	100644 blob $(test_oid 003)	foo
 	EOF
 	tree=$(git mktree --missing <broken-tree) &&
-	git gc 2>stderr &&
+	git gc -q 2>stderr &&
 	git cat-file -e $tree &&
 	test_must_be_empty stderr
 '
 
 test_expect_success 'do not complain about existing broken links (tag)' '
-	cat >broken-tag <<-\EOF &&
-	object 0000000000000000000000000000000000000004
+	cat >broken-tag <<-EOF &&
+	object $(test_oid 004)
 	type commit
 	tag broken
 	tagger whatever <whatever@example.com> 1234 -0000
@@ -162,7 +162,7 @@ test_expect_success 'do not complain about existing broken links (tag)' '
 	this is a broken tag
 	EOF
 	tag=$(git hash-object -t tag -w broken-tag) &&
-	git gc 2>stderr &&
+	git gc -q 2>stderr &&
 	git cat-file -e $tag &&
 	test_must_be_empty stderr
 '