omit SVN requirement with DOWNLOAD_GAMEPACKS=no

this is to workaround github actions build error: svn.exe is present, but access returns code 127

.github/workflows/build.yml

@@ -27,7 +27,7 @@ jobs:
     steps:
     - uses: msys2/setup-msys2@v2
       with:
-        install: ${{ matrix.prefix }}-qt5-base ${{ matrix.prefix }}-libxml2 svn git
+        install: ${{ matrix.prefix }}-qt5-base ${{ matrix.prefix }}-libxml2 git
         msystem: ${{ matrix.msystem }}
         path-type: minimal
         release: false

Makefile

@@ -337,7 +337,7 @@ dependencies-check:
 	checkbinary pkg-config "$(PKGCONFIG)"; \
 	checkbinary unzip "$(UNZIPPER)"; \
 	checkbinary git-core "$(GIT)"; \
-	checkbinary subversion "$(SVN)"; \
+	[ "$(DOWNLOAD_GAMEPACKS)" = "yes" ] || [ "$(DOWNLOAD_GAMEPACKS)" = "all" ] && checkbinary subversion "$(SVN)"; \
 	checkbinary wget "$(WGET)"; \
 	[ "$(OS)" = "Win32" ] && checkbinary mingw32 "$(WINDRES)"; \
 	[ -n "$(LDD)" ] && checkbinary libc6 "$(LDD)"; \