Fetch SQL compiler using https instead of git.

ryzhyk · web-flow · commit 70e30f0c21ee · 2023-03-08T17:48:40.000-08:00
Cargo is unable to cope with a submodule dependency using the `git://` URL (due to some limitations of its git client library).  Unfortunately, this only surfaced once the change was merged into `main`.
diff --git a/.gitmodules b/.gitmodules
@@ -1,3 +1,3 @@
 [submodule "sql-to-dbsp-compiler"]
 	path = sql-to-dbsp-compiler
-	url = git@github.com:vmware/sql-to-dbsp-compiler.git
+	url = https://github.com/vmware/sql-to-dbsp-compiler.git
