release message needs to be escaped

Just tried to release a package with a release message ending in '$', and got this:

```
12:53:24 ERROR ReleaseVCSError: command failed: /sw/resources/suites/global/core/linux_x86_64_CentOS-7/ver/160/bin/git tag -a mlambda-3.1.4 -m '- don'"'"'t set mlambda loglevel to INFO if it'"'"'s already set lower (eg DEBUG) - better logging for debugging - tag manifest lo$'
/tmp/rez_context_hTpGfD/rez-shell.sh: line 8: syntax error near unexpected token `('
/tmp/rez_context_hTpGfD/rez-shell.sh: line 8: `git tag -a mlambda-3.1.4 -m - don't set mlambda loglevel to INFO if it's already set lower (eg DEBUG) - better logging for debugging - tag manifest lo$'
```

Start with the release flow that constructs the `git tag -a ... -m` command and inspect the generated `/tmp/rez_context_hTpGfD/rez-shell.sh` shown in the report. Reproduce a release message ending in `$`; done means the tag command runs without the shell syntax error and preserves the complete message.

Written by the indexing model from the issue text.