Update to Alpine 3.11 and fix version info in CI builds

mautrix_telegram/get_version.py

@@ -1,4 +1,5 @@
 import subprocess
+import shutil
 import os
 
 from . import __version__
@@ -15,7 +16,7 @@ def run(cmd):
     return subprocess.check_output(cmd, stderr=subprocess.DEVNULL, env=cmd_env)
 
 
-if os.path.exists(".git"):
+if os.path.exists(".git") and shutil.which("git"):
     try:
         git_revision = run(["git", "rev-parse", "HEAD"]).strip().decode("ascii")
         git_revision_url = f"https://github.com/tulir/mautrix-telegram/commit/{git_revision}"
@@ -26,15 +27,20 @@ if os.path.exists(".git"):
 
     try:
         git_tag = run(["git", "describe", "--exact-match", "--tags"]).strip().decode("ascii")
-        git_tag_url = f"https://github.com/tulir/mautrix-telegram/releases/tag/{git_tag}"
     except (subprocess.SubprocessError, OSError):
         git_tag = None
-        git_tag_url = None
+elif os.environ.get("CI_SERVER", "no") == "yes":
+    git_revision = os.environ["CI_COMMIT_SHA"]
+    git_revision_url = f"https://github.com/tulir/mautrix-telegram/commit/{git_revision}"
+    git_revision = git_revision[:8]
+    git_tag = os.environ.get("CI_COMMIT_TAG", None)
 else:
     git_revision = "unknown"
     git_revision_url = None
     git_tag = None
-    git_tag_url = None
+
+git_tag_url = (f"https://github.com/tulir/mautrix-telegram/releases/tag/{git_tag}"
+               if git_tag else None)
 
 if git_tag and __version__ == git_tag[1:].replace("-", ""):
     version = __version__