CI: Check MSRV without git feature enabled

git2-rs MSRV policy is to only support latest stable rust (see
https://github.com/rust-lang/git2-rs#rust-version-requirements), so it
does not make sense to run our MSRV tests with git enabled.

tests/snapshot_tests.rs

@@ -1,13 +1,13 @@
+#[cfg(feature = "git")]
 mod tester;
 
-use crate::tester::BatTester;
-
 macro_rules! snapshot_tests {
     ($($test_name: ident: $style: expr,)*) => {
         $(
             #[test]
+            #[cfg(feature = "git")]
             fn $test_name() {
-                let bat_tester = BatTester::default();
+                let bat_tester = tester::BatTester::default();
                 bat_tester.test_snapshot(stringify!($test_name), $style);
             }
         )*