Fix Alpine and musl release builds

Alpine containers have no bash; remove global shell: bash default
so each job uses its own shell (sh for Alpine, bash for others).

Alpine abuild requires gzipped man pages and rejects files under
/lib.  Install systemd unit to /usr/lib/systemd/system and gzip
the man page in the APKBUILD.

Author: renaudallard

.github/workflows/release.yml

@@ -20,10 +20,6 @@ env:
   DEBIAN_FRONTEND: noninteractive
   RPMBUILD_TOPDIR: /tmp/rpmbuild
 
-defaults:
-  run:
-    shell: bash
-
 jobs:
   detect-versions:
     name: Detect distro versions

alpine/APKBUILD

@@ -18,5 +18,6 @@ check() {
 }
 
 package() {
-	make install DESTDIR="$pkgdir" PREFIX=/usr UNITDIR=/lib/systemd/system
+	make install DESTDIR="$pkgdir" PREFIX=/usr UNITDIR=/usr/lib/systemd/system
+	gzip "$pkgdir"/usr/share/man/man8/thinproxy.8
 }