Don’t try to install something when running from uninstalled source (#12246).

Original patch by Tshepang Lekhonkhobe.
diff --git a/Misc/ACKS b/Misc/ACKS
index 900fae7..de5410c 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -550,6 +550,7 @@
 Robert Lehmann
 Petri Lehtinen
 Luke Kenneth Casson Leighton
+Tshepang Lekhonkhobe
 Marc-Andre Lemburg
 John Lenton
 Christopher Tur Lesniewski-Laas