[setup] Bump fallback version

When installing FuseSoC from OpenTitan -- that is, with

    pip install -r python-requirements.txt

Pip currently gets instructed to download

    https://github.com/lowRISC/fusesoc/archive/refs/tags/ot-0.5.zip

However, that downloaded version **currently presents itself as version
`0.4.dev0`**, to Pip as well as in `fusesoc --version`.  This is
problematic in at least two ways:

1. Because Pip gets told that it downloaded version 0.4, it can prefer
   to use a locally cached archive (and I've seen it doing that!) that
   is *really* version 0.4, causing the update to fail even though the
   user thinks they just updated FuseSoC.

2. Users have no way of distinguishing between versions 0.4 and 0.5 from
   the command line, which makes debugging difficult.

I don't know the root cause for why `use_scm_version` doesn't work as
expected, but this hotfixes the fallback version to the currently tagged
version.  We then need to update the Git tag to this commit and update
the hash in the OpenTitan repo.

setup.py

@@ -17,7 +17,7 @@ def read(fname):
     use_scm_version={
         "relative_to": __file__,
         "write_to": "fusesoc/version.py",
-        "fallback_version": "0.4.dev0",
+        "fallback_version": "0.5.dev0",
     },
     author="Olof Kindgren",
     author_email="[email protected]",