kokoro: Remove extra / in architecture replacement

The trailing slash was accidentally introduced in 10d901d when
reversing the replacement order. The slash causes the new file name to
have an extra directory in it, which doesn't exist, so the copy command
then fails.

Fixes #12862

Author: ejona86

buildscripts/kokoro/upload_artifacts.sh

@@ -43,7 +43,7 @@ LOCAL_OTHER_ARTIFACTS="$KOKORO_GFILE_DIR"/github/grpc-java/artifacts/
 # from macos job:
 [[ "$(find "$LOCAL_MVN_ARTIFACTS" -type f -iname 'protoc-gen-grpc-java-*-osx-aarch_64.exe' | wc -l)" != '0' ]]
 # copy the universal binaries to x86, as they work on both architectures
-find "$LOCAL_MVN_ARTIFACTS" -type f -iname 'protoc-gen-grpc-java-*-osx-aarch_64.exe*' -exec bash -c 'cp "${0}" "${0/aarch/x86/}"' {} \;
+find "$LOCAL_MVN_ARTIFACTS" -type f -iname 'protoc-gen-grpc-java-*-osx-aarch_64.exe*' -exec bash -c 'cp "${0}" "${0/aarch/x86}"' {} \;
 
 # from windows job:
 [[ "$(find "$LOCAL_MVN_ARTIFACTS" -type f -iname 'protoc-gen-grpc-java-*-windows-x86_64.exe' | wc -l)" != '0' ]]