Build all source packages in a separate build job

See https://github.com/msys2/msys2-autobuild/issues/69

Building source packages requires git etc to be installed, but
ideally we wouldn't pollute the builder with extra packages that
it doesn't explicitly require.

To avoid this build msys and mingw source packages in a separate job.

autobuild.py

@@ -1094,26 +1094,24 @@ def get_job_meta() -> List[Dict[str, Any]]:
                 "runner": ["Windows", "ARM64", "autobuild"]
             }
         }, {
-            "build-types": ["msys", "msys-src"],
+            "build-types": ["msys"],
             "matrix": {
-                "packages": "base-devel VCS",
+                "packages": "base-devel",
                 "build-args": "--build-types msys,msys-src",
                 "name": "msys",
                 "runner": hosted_runner
             }
+        }, {
+            "build-types": ["msys-src", "mingw-src"],
+            "matrix": {
+                "packages": "base-devel VCS",
+                "build-args": "--build-types msys-src,mingw-src",
+                "name": "src",
+                "runner": hosted_runner
+            }
         }
     ]
 
-    # The job matching MINGW_SRC_ARCH should also build mingw-src
-    for meta in job_meta:
-        if Config.MINGW_SRC_ARCH in meta["build-types"]:
-            meta["build-types"].append("mingw-src")
-            meta["matrix"]["build-args"] = meta["matrix"]["build-args"] + ",mingw-src"
-            meta["matrix"]["packages"] = meta["matrix"]["packages"] + " VCS"
-            break
-    else:
-        raise Exception("Didn't find arch for building mingw-src")
-
     return job_meta