Prefer executing these files using the OSS-Fuzz or `python` command
methods outlined in the `fuzzing/README`.

Based on feedback and discussion on:
gitpython-developers#1901

This script is meant to be sourced by the OSS-Fuzz file of the same
name, rather than executed directly. The shebang may lead to the
incorrect assumption that the script is meant for direct execution.
Replacing it with this directive instructs ShellCheck to treat
the script as a Bash script, regardless of how it is executed.

Based @EliahKagan's suggestion and feedback on:
gitpython-developers#1901

This script is executed directly, not sourced as is the case with
`build.sh`, so it should have an executable bit set to avoid ambiguity.

Based @EliahKagan's suggestion and feedback on:
gitpython-developers#1901

- Make the link text for the OSS-Fuzz test status URL more descriptive
- Fix capitalization of GitPython repository name

Based @EliahKagan's suggestion and feedback on:
gitpython-developers#1901

Replaces the null character delimiter `-d $'\0'` with the simpler
empty string `-d ''` in the fuzzing harness build loop.

This changes leverages the Bash `read` builtin behavior to avoid
unnecessary complexity and improving script readability.

Based @EliahKagan's suggestion and feedback on:
gitpython-developers#1901