ci: fix Docker build

This fixes some issues with the Docker build process

  * missing `git` in wheel build process - pip requires Git to pull
    dependencies expressed as `foo @ git+https://...`.

  * pip upgrade before building - it was disabled with an extra `echo`
    Thanks to @ahpaleus for reporting this!

  * final image installation - pip insists on rebuilding git-referenced
    dependencies, so this installs the wheels directly with `--no-deps`
    to get the desired behavior.

Dockerfile

@@ -2,6 +2,7 @@
 FROM ubuntu:jammy AS python-wheels
 RUN apt-get update && DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends \
     gcc \
+    git \
     python3-dev \
     python3-pip \
   && rm -rf /var/lib/apt/lists/*
@@ -9,7 +10,7 @@ RUN apt-get update && DEBIAN_FRONTEND=noninteractive apt-get install -y --no-ins
 COPY . /slither
 
 RUN cd /slither && \
-    echo pip3 install --no-cache-dir --upgrade pip && \
+    pip3 install --no-cache-dir --upgrade pip && \
     pip3 wheel -w /wheels . solc-select pip setuptools wheel
 
 
@@ -44,7 +45,7 @@ ENV PATH="/home/slither/.local/bin:${PATH}"
 
 # no-index ensures we install the freshly-built wheels
 RUN --mount=type=bind,target=/mnt,source=/wheels,from=python-wheels \
-    pip3 install --user --no-cache-dir --upgrade --no-index --find-links /mnt pip slither-analyzer solc-select
+    pip3 install --user --no-cache-dir --upgrade --no-index --find-links /mnt --no-deps /mnt/*.whl
 
 RUN solc-select install 0.4.25 && solc-select use 0.4.25