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GH-44749: [CI][Dev] Apply ShellCheck lint to ci/scripts/c_glib_test.sh (#44750)

### Rationale for this change

```console
$ pre-commit run --show-diff-on-failure --color=always --all-files shellcheck
ShellCheck v0.10.0.......................................................Failed
- hook id: shellcheck
- exit code: 1

In ci/scripts/c_glib_test.sh line 25:
: ${ARROW_GLIB_VAPI:=true}
  ^----------------------^ SC2223 (info): This default assignment may cause DoS due to globbing. Quote it.

In ci/scripts/c_glib_test.sh line 37:
pushd ${source_dir}
      ^-----------^ SC2086 (info): Double quote to prevent globbing and word splitting.

Did you mean:
pushd "${source_dir}"

In ci/scripts/c_glib_test.sh line 54:
pushd ${build_dir}
      ^----------^ SC2086 (info): Double quote to prevent globbing and word splitting.

Did you mean:
pushd "${build_dir}"

For more information:
  https://www.shellcheck.net/wiki/SC2086 -- Double quote to prevent globbing ...
  https://www.shellcheck.net/wiki/SC2223 -- This default assignment may cause...
```

### What changes are included in this PR?

* Add missing quotes.

### Are these changes tested?

Yes.

### Are there any user-facing changes?

No.
* GitHub Issue: #44749

Authored-by: Sutou Kouhei <kou@clear-code.com>
Signed-off-by: Jacob Wujciak-Jens <jacob@wujciak.de>