shallow clones: fetch tags shallowly too

It turns out that git fetch origin tag will clone the full repository unless it is also given --depth=1 as an argument.

This commit amends this oversight, ensuring source-repository-package stanzas with any tag don't have to fall back to fetch unnecessary information (which is coincidentally much faster)

cabal-install/src/Distribution/Client/VCS.hs

@@ -583,7 +583,7 @@ vcsGit =
           --
           -- Option 2 is what Cabal has done historically, and we're keeping it
           -- for now. Option 1 is possible but seems to have little benefit.
-          git localDir ("fetch" : verboseArg ++ ["origin", ref])
+          git localDir ("fetch" : verboseArg ++ ["--depth=1", "origin", ref])
           pure "FETCH_HEAD"
         Just ref
           | otherwise ->