Add very crude parsing of "repomd.xml"

This gives us more accurate version scraping that's not reliant on the cache of the HTML file listing (which instead matches how `yum`/`dnf` query these version numbers, so should stay in sync better).

This should fix our issues with CI sometimes returning a mismatch in 8.0 versions.

**However**, this *causes* a mismatch in 5.7 versions because the latest 5.7 release (that we were not picking up before due to the aforementioned HTML caching but are now with this updated code) is apparently not built/released for Debian (https://dev.mysql.com/downloads/mysql/), so we also need to decide whether we're going to introduce Debian/Oracle version skew or perhaps deprecate/remove the Debian variants of 5.7 (which is ostensibly EOL in ~3 months).

versions.sh

@@ -23,7 +23,28 @@ fetch_rpm_versions() {
 	local oracleVersion="$1"; shift
 	local package="$1"; shift
 
-	curl -fsSL "$repo/$arch/" 2>/dev/null \
+	local baseurl="$repo/$arch"
+
+	# *technically*, we should parse "repodata/repomd.xml", look for <data type="primary">, and use the <location href="..."> value out of it, but parsing XML is not trivial with only basic tools, it turns out, so instead we rely on MySQL's use of "*-primary.xml.*" as the filename we're after 👀
+	local primaryLocation
+	primaryLocation="$(
+		# 2>/dev/null in case "$arch" doesn't exist in "$repo" 🙈
+		curl -fsSL "$baseurl/repodata/repomd.xml" 2>/dev/null \
+			| grep -oE 'href="[^"]+-primary[.]xml([.]gz)?"' \
+			| cut -d'"' -f2
+	)" || return 1
+	[ -n "$primaryLocation" ] || return 1
+
+	local decompressor='cat'
+	case "$primaryLocation" in
+		*.gz) decompressor='gunzip' ;;
+		*.xml) ;;
+		*) echo >&2 "error: unknown compression (from '$baseurl'): $primaryLocation"; exit 1 ;;
+	esac
+
+	# again, *technically* we should properly parse XML here, but y'know, it's complicated
+	curl -fsSL "$baseurl/$primaryLocation" \
+		| "$decompressor" \
 		| grep -oE '"'"$package"'-[0-9][^"]+[.]el'"$oracleVersion"'[.]'"$arch"'[.]rpm"' \
 		| sed -r 's/^"'"$package-|[.]$arch[.]rpm"'"$//g' \
 		| sort -rV
@@ -111,6 +132,10 @@ for version in "${versions[@]}"; do
 		export bashbrewArch
 		doc="$(jq <<<"$doc" -c '.oracle.architectures = (.oracle.architectures + [ env.bashbrewArch ] | sort)')"
 	done
+	if [ -z "$rpmVersion" ]; then
+		echo >&2 "error: missing version for '$version'"
+		exit 1
+	fi
 	baseVersion="$(jq <<<"$doc" -r '.version // ""')"
 	# example 8.0.22-1.el7 => 8.0.22
 	oracleBaseVersion="${rpmVersion%-*}"