Fix #2734: adjust bounds to compile on 9.6

The whole test suite passes for me, including prop_checkOverwrittenExitCode8,
and I get the same set of findings with this build and shellcheck.net on
tools/testing/selftests/net/icmp_redirect.sh.

Add fish to the badShells list

Document Trunk Check integration

ShellCheck is temporarily broken by
https://github.com/haskell/fgl/commit/c8f56c18242b0c3e916892c5db56a609ec396637

Trunk Check is a universal linter which integrates with a wide variety of linters and formatters, `shellcheck` included.

We're big fans of `shellcheck` and figured that you might find our tool to be interesting enough to include it in the integrations list.

This release is dedicated to Mindustry: the most fun you can
have with open source (outside of shell scripting of course).

Fixes the following error:

    src/ShellCheck/CFGAnalysis.hs:1394:40: error:
	* Couldn't match expected type `[S.Set a]'
		      with actual type `M.Map String FunctionValue'
	* In the second argument of `($)', namely
	    `mapStorage $ sFunctionTargets state'
	  In the expression: S.unions $ mapStorage $ sFunctionTargets state
	  In an equation for `declaredFuncs':
	      declaredFuncs = S.unions $ mapStorage $ sFunctionTargets state
	* Relevant bindings include
	    declaredFuncs :: S.Set a
	      (bound at src/ShellCheck/CFGAnalysis.hs:1394:13)

Dash throws an error if the read command isn't supplied a variable name.

Permit colon after exec

This reverts commit 5202072a.

Fix false positive for SC2312 when using `time`

ShellCheck throws warning SC2093 when a script contains commands that could never be executed because they are after an `exec`.  Command `:` does nothing, so add it to the list of commands that don’t trigger this warning.