Install kubectl from alpine edge in Dockerfile

Dockerfile

@@ -2,7 +2,7 @@
 FROM alpine:3.14
 
 LABEL name="Stackspin management"
-LABEL version="4.4"
+LABEL version="4.5"
 LABEL vendor1="Greenhost"
 
 ENV TAIKO_SKIP_CHROMIUM_DOWNLOAD=true
@@ -10,11 +10,12 @@ ENV TAIKO_BROWSER_PATH=/usr/bin/chromium-browser
 ENV TAIKO_BROWSER_ARGS=--no-sandbox,--start-maximized,--disable-dev-shm-usage,--ignore-certificate-errors
 
 ADD https://github.com/fluxcd/flux2/releases/download/v0.20.1/flux_0.20.1_linux_amd64.tar.gz /tmp/
-# Download kubectl until it's packaged in alpine > 3.14
-ADD https://dl.k8s.io/release/v1.21.0/bin/linux/amd64/kubectl /usr/local/bin/
 COPY ./test/pytest/le-staging-bundle.pem /usr/local/share/ca-certificates/le-staging-bundle.pem
 COPY ./requirements.txt /requirements.txt
 RUN \
+  # Install kubectl from alpine edge until 3.15 is released
+  apk --no-cache add kubectl=~1.22.3-r0 \
+    --repository=http://dl-cdn.alpinelinux.org/alpine/edge/testing && \
   apk --no-cache add \
     bash=~5.1.4-r0 \
     cargo=~1.52.1-r1 \
@@ -39,7 +40,6 @@ RUN \
     yq=4.6.3-r2 && \
   rm -rf /var/cache/* && \
   mkdir /var/cache/apk && \
-  chmod a+x /usr/local/bin/* && \
   update-ca-certificates && \
   pip install --no-cache-dir --ignore-installed six -r /requirements.txt && \
   ln -s /usr/bin/python3 /usr/bin/python && \