fix: explicit https flutter fetch (#383)

* fix: explicit https source

* try again

Author: damian-molinski

earthly/flutter/Earthfile

@@ -22,6 +22,8 @@ INSTALL_FLUTTER:
         # And remove below lines to the end of this ELSE-IF block:
         GIT CLONE https://github.com/flutter/flutter.git /usr/local/flutter
         WORKDIR /usr/local/flutter
+        # Explicitly fetch from the 'origin' remote (HTTPS). Otherwise may attempt SSH-a
+        RUN git remote set-url origin https://github.com/flutter/flutter.git
         RUN git fetch --unshallow
         RUN git checkout tags/$version
         WORKDIR /