revert(3p/git): Revert merge of git upstream at v2.26.2

This causes cgit to serve error pages, which is undesirable.

This reverts commit 5229c9b232, reversing
changes made to f2b211131f.

third_party/git/ci/lib.sh

@@ -34,11 +34,6 @@ save_good_tree () {
 # successfully before (e.g. because the branch got rebased, changing only
 # the commit messages).
 skip_good_tree () {
-	if test "$TRAVIS_DEBUG_MODE" = true
-	then
-		return
-	fi
-
 	if ! good_tree_info="$(grep "^$(git rev-parse $CI_COMMIT^{tree}) " "$good_trees_file")"
 	then
 		# Haven't seen this tree yet, or no cached good trees file yet.
@@ -131,6 +126,7 @@ then
 		echo "$SYSTEM_TASKDEFINITIONSURI$SYSTEM_TEAMPROJECT/_build/results?buildId=$1"
 	}
 
+	BREW_INSTALL_PACKAGES=gcc@8
 	export GIT_PROVE_OPTS="--timer --jobs 10 --state=failed,slow,save"
 	export GIT_TEST_OPTS="--verbose-log -x --write-junit-xml"
 	MAKEFLAGS="$MAKEFLAGS --jobs=10"
@@ -155,7 +151,7 @@ fi
 
 export DEVELOPER=1
 export DEFAULT_TEST_TARGET=prove
-export GIT_TEST_CLONE_2GB=true
+export GIT_TEST_CLONE_2GB=YesPlease
 
 case "$jobname" in
 linux-clang|linux-gcc)
@@ -164,7 +160,7 @@ linux-clang|linux-gcc)
 		export CC=gcc-8
 	fi
 
-	export GIT_TEST_HTTPD=true
+	export GIT_TEST_HTTPD=YesPlease
 
 	# The Linux build installs the defined dependency versions below.
 	# The OS X build installs much more recent versions, whichever
@@ -181,7 +177,7 @@ linux-clang|linux-gcc)
 osx-clang|osx-gcc)
 	if [ "$jobname" = osx-gcc ]
 	then
-		export CC=gcc-9
+		export CC=gcc-8
 	fi
 
 	# t9810 occasionally fails on Travis CI OS X