Fix typos (#7050)

Uses https://en.wikipedia.org/wiki/Wikipedia:Lists_of_common_misspellings/For_machines to find likely typos, with https://github.com/bwignall/typochecker to help automate the checking.
diff --git a/php/generate_descriptor_protos.sh b/php/generate_descriptor_protos.sh
index 372ad69..f636cc0 100755
--- a/php/generate_descriptor_protos.sh
+++ b/php/generate_descriptor_protos.sh
@@ -1,6 +1,6 @@
 #!/usr/bin/env bash
 
-# Run this script to regenerate desriptor protos after the protocol compiler
+# Run this script to regenerate descriptor protos after the protocol compiler
 # changes.
 
 if test ! -e src/google/protobuf/stubs/common.h; then