ci: Update Android and mingw CI images

Fedora 29 is no longer available, and I need to rebuild these images so
libpcre is pre-downloaded as a subproject.

Update them to Fedora 31, which is what we use in `fedora.Dockerfile`.
This should allow some blobs to be shared in the container repository.

This isn’t the latest Fedora release, but I don’t want to go through the
hassle of updating all the CI images to F33 right now in addition to
updating the subproject caches.

`python-unversioned-command` is needed because the Android NDK calls
`python` without a version number. F29 must have installed this already.
The Android NDK setup appears to be OK with Python 3.

Signed-off-by: Philip Withnall <pwithnall@endlessos.org>

Helps: #962

.gitlab-ci/android-ndk.Dockerfile

@@ -1,4 +1,4 @@
-FROM fedora:28
+FROM fedora:31
 
 RUN dnf -y install \
     autoconf \
@@ -44,6 +44,7 @@ RUN dnf -y install \
     ncurses-compat-libs \
     ninja-build \
     pcre-devel \
+    python-unversioned-command \
     python3 \
     python3-pip \
     python3-wheel \

.gitlab-ci/mingw.Dockerfile

@@ -1,4 +1,4 @@
-FROM fedora:29
+FROM fedora:31
 
 RUN dnf -y install \
     bindfs \