This was found useful by @Bramas when building a Dockerfile of the web app
itself. See https://github.com/ente-io/ente/pull/1065.
Now, the GIT_SHA environment variable can just be undefined if we're not in a
git repository, and the code using it deals with that case explicitly.
**Tested by**
Temporarily inverted the isDevBuild flag, tehn
1. Ran the build normally and verified that the SHA continued to appear in the logs.
2. Ran the build after copying to a standalone folder without an associated git
repository and verified that the SHA was skipped without causing the build to
fail.
26b162c8dc