CICD: Improve Workflows.

Make multiple improvements to the existing workflows:
- create a shared custom action to deal with version number tracking
  and generation;
- use this action to add the branch name to the version for pull
  request builds;
- create a shared workflow for all debian-ish builds to avoid re-use
  by copy / paste;
- remove potential security risks by eliminating the use of
  pre-evaluated expressions (`${{ ... }}`) inside scripts;
- update outdated GitHub action versions;
- improve the consistency by renaming scripts acording to have a `.sh`
  extension;
- improve naming of generated artefacts for pull requests to include
  the correct version.

@dirkh: Unfortunately this is potentially going to break builds when it is
merged, as there is no good way to 'test' a merge build short of
merging.
We'll just have to deal with the fallout of it in a follow-up pull
request.

Signed-off-by: Michael Keller <github@ike.ch>

scripts/check-version.sh

@@ -0,0 +1,95 @@
+#!/bin/sh
+
+# $1	- version string
+# options:
+#	-c	colored grep (implies -d)
+#	-d	debug
+#	-r	release (exit status error; when called from Makefile)
+
+# To validate relevant files are up to date, you would run the script
+# from command line before tagging:
+#
+#	$ scripts/check-version.sh -cr <tag>
+
+set -eu
+#set -x
+
+# You would typically add/remove files to/from the list
+files="Documentation/user-manual.txt Makefile README.md ReleaseNotes/ReleaseNotes.txt"
+
+whine() {
+	echo "$0: $*" >&2
+}
+
+croak() {
+	whine "$*"
+	exit 1
+}
+
+color=n
+debug=n
+release=n
+while getopts cdr opt; do
+	case $opt in
+		c)
+			color=y
+			debug=y
+			;;
+		d)
+			debug=y
+			;;
+		r)
+			release=y
+			;;
+		*)
+			croak "invalid option"
+			;;
+	esac
+done
+shift $(($OPTIND - 1))
+
+if [ $debug = y ]; then
+	opts=-n
+else
+	opts=-q
+fi
+[ $color = n ] || opts="${opts:+$opts }--color"
+
+v=${1:-}
+v=${v#v}
+case $v in
+	*-*)
+		# Ignore development versions
+		if [ $release = y ]; then
+			croak "'$v' not a release tag"
+		else
+			exit 0
+		fi
+		;;
+	''|*[!.0-9]*)
+		croak "invalid version string '$v'"
+		;;
+esac
+whine "checking for version $v"
+
+saveIFS=$IFS
+IFS=.
+set -- $v
+IFS=$saveIFS
+v=
+while [ $# -gt 0 ]; do
+	v=${v:+$v\\.}$1
+	shift
+done
+
+sts=0
+for f in $files; do
+	grep	-EH $opts \
+		-e "(VERSION=|[Ss]ubsurface[[:blank:]]+)?\<v?$v[.0-9]*\>" \
+		$f || {
+		[ $release != y ] || sts=1
+		whine "'$f' may need updating"
+	}
+done
+
+exit $sts