[CI] Upgrade sccache version to 0.7.*

Sccache was previously pinned at version 0.3.3, however, there has
recently been an issue when installing some of its dependencies:

```
error[E0277]: expected a `Fn(reqwest::Request, &'a mut task_local_extensions::extensions::Extensions, reqwest_middleware::Next<'a>)` closure, found `RetryAfterMiddleware`
```

Upgrading the version of sccache to the latest seems to resolve this
error.

Change-Id: Ie292c1189de2ed8464fe1b78e672d7f53a083dff

docker/install/ubuntu_install_sccache.sh

@@ -20,7 +20,7 @@ set -e
 set -u
 set -o pipefail
 
-cargo install --version 0.3.3 sccache
+cargo install --version 0.7.* sccache
 
 # The docs specifically recommend hard links: https://github.com/mozilla/sccache#known-caveats
 mkdir /opt/sccache