Update Inno Setup download source and hash validation

- Switch download source to GitHub releasess since the creator remove 6.4.1 and downloads in general from the original site
- Update hash algorithm from SHA-512 to SHA-256 since that's what github releases provides
- Adjust script variables for enhanced clarity.

containers/build-release/Dockerfile

diff --git a/containers/build-release/Dockerfile b/containers/build-release/Dockerfile
index 4d83d78..ef6cd68 100644
--- a/containers/build-release/Dockerfile
+++ b/containers/build-release/Dockerfile
@@ -61,10 +61,11 @@
 # configuration expects it--different wine configurations could install it
 # somewhere else.
 RUN \
+  INNO_SETUP_TAG="6_4_1" && \
   INNO_SETUP_EXE="innosetup-6.4.1.exe" && \
-  EXPECTED_SHA=5dfc9999e2feafa28754baaf80cf73ac96414228b94a1132a919554a822c892810197305d9355885b9ac408c214691cd45279fc2df3a891fbebc4f8eb86bac87 && \
-  curl -L https://files.jrsoftware.org/is/6/$INNO_SETUP_EXE -o $INNO_SETUP_EXE && \
-  echo "$EXPECTED_SHA $INNO_SETUP_EXE" | sha512sum --quiet -c - && \
+  EXPECTED_SHA=f41760e1f1ae15d2089bb6ab162e21720b92ae7506ed70667b39200063d68e34 && \
+  curl -L https://github.com/jrsoftware/issrc/releases/download/is-$INNO_SETUP_TAG/$INNO_SETUP_EXE -o $INNO_SETUP_EXE && \
+  echo "$EXPECTED_SHA $INNO_SETUP_EXE" | sha256sum --quiet -c - && \
   winetricks -q win10 && \
   xvfb-run wine $INNO_SETUP_EXE /VERYSILENT /SUPPRESSMSGBOXES /TASKS= '/DIR=C:\\Program Files (x86)\\Inno Setup 6' && \
   rm $INNO_SETUP_EXE