libfetchers: Restore plain git inputs recognition

Accidentally broken in dbc235cc62.
Adds a bit of tests for this, even though this protocol is mostly deprecated
everywhere.

(cherry picked from commit ade3d5d746)

src/libfetchers/git.cc

@@ -164,8 +164,7 @@ struct GitInputScheme : InputScheme
 {
     std::optional<Input> inputFromURL(const Settings & settings, const ParsedURL & url, bool requireTree) const override
     {
-        auto parsedScheme = parseUrlScheme(url.scheme);
-        if (parsedScheme.application != "git")
+        if (url.scheme != "git" && parseUrlScheme(url.scheme).application != "git")
             return {};
 
         auto url2(url);

src/libflake-tests/flakeref.cc

@@ -199,6 +199,28 @@ INSTANTIATE_TEST_SUITE_P(
             .description = "flake_id_ref_branch_ignore_empty_segments_ref_rev",
             .expectedUrl = "flake:nixpkgs/branch/2aae6c35c94fcfb415dbe95f408b9ce91ee846ed",
         },
+        InputFromURLTestCase{
+            .url = "git://somewhere/repo?ref=branch",
+            .attrs =
+                {
+                    {"type", Attr("git")},
+                    {"ref", Attr("branch")},
+                    {"url", Attr("git://somewhere/repo")},
+                },
+            .description = "plain_git_with_ref",
+            .expectedUrl = "git://somewhere/repo?ref=branch",
+        },
+        InputFromURLTestCase{
+            .url = "git+https://somewhere.aaaaaaa/repo?ref=branch",
+            .attrs =
+                {
+                    {"type", Attr("git")},
+                    {"ref", Attr("branch")},
+                    {"url", Attr("https://somewhere.aaaaaaa/repo")},
+                },
+            .description = "git_https_with_ref",
+            .expectedUrl = "git+https://somewhere.aaaaaaa/repo?ref=branch",
+        },
         InputFromURLTestCase{
             // Note that this is different from above because the "flake id" shorthand
             // doesn't allow this.