ci: fix docker image version

Author: Helias

Dockerfile

@@ -1,10 +1,11 @@
-FROM linuxserver/calibre:latest
+FROM linuxserver/calibre:5.38.0
 
 WORKDIR /epub_to_pdf
 
 RUN apt-get -y update \
-    && apt -y install python3-pip \
-    && pip3 install python-telegram-bot
+    && apt -y install python3-pip
+RUN python3 -m pip install python-telegram-bot
+
 COPY . .
 
 CMD ["python3", "main.py"]