Enable mipsel+libc tests on CI

Author: LemonBoy

test/tests.zig

@@ -140,6 +140,16 @@ const test_targets = [_]TestTarget{
             },
         },
     },
+    TestTarget{
+        .target = Target{
+            .Cross = CrossTarget{
+                .os = .linux,
+                .arch = .mipsel,
+                .abi = .musl,
+            },
+        },
+        .link_libc = true,
+    },
 
     TestTarget{
         .target = Target{