GHA: add shellcheck job and fix warnings, shell tidy-ups

Reviewed-by: Daniel Stenberg
Closes #13307

copyright: update all copyright lines and remove year ranges

- they are mostly pointless in all major jurisdictions
- many big corporations and projects already don't use them
- save

copyright: update all copyright lines and remove year ranges

- they are mostly pointless in all major jurisdictions
- many big corporations and projects already don't use them
- saves us from pointless churn
- git keeps history for us
- the year range is kept in COPYING

checksrc is updated to allow non-year using copyright statements

Closes #10205

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copyright: make repository REUSE compliant

Add licensing and copyright information for all files in this repository. This
either happens in the file itself as a comment header or in the

copyright: make repository REUSE compliant

Add licensing and copyright information for all files in this repository. This
either happens in the file itself as a comment header or in the file
`.reuse/dep5`.

This commit also adds a Github workflow to check pull requests and adapts
copyright.pl to the changes.

Closes #8869

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Makefile: fix "make ca-firefox"

Closes #8804

scripts: move three scripts from lib/ to scripts/

Move checksrc.pl, firefox-db2pem.sh and mk-ca-bundle.pl since they don't
particularly belong in lib/

Also created an EXTRA_DIST

scripts: move three scripts from lib/ to scripts/

Move checksrc.pl, firefox-db2pem.sh and mk-ca-bundle.pl since they don't
particularly belong in lib/

Also created an EXTRA_DIST= in scripts/Makefile.am instead of specifying
those files in the root Makefile.am

Closes #8625

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