Restore RHEL 8 entries on the Qt5/Qt6-selecting rosdep keys

[nbbrooks]

The seven Qt5/Qt6-selecting rosdep keys added in #50896 and #50897 all declare rhel: '8': null, so any package depending on them cannot be released for RHEL 8. This PR fills in the RHEL 8 entries with the same Qt5 packages already used for RHEL 9.

How this surfaced

Releasing rviz_visual_tools 4.2.0 to Humble, which switched to qt-base-dev/libqtwidgets to pick up Qt6 on Resolute. Bloom's rosrpm generator for rhel:8:

Could not resolve rosdep key 'libqtwidgets' for distro '8':
[libqtwidgets] defined as "not available" for OS version [8]
Failed to resolve libqtwidgets on rhel:8 with: Error running generator:
  Failed to resolve rosdep key 'libqtwidgets', aborting.

The same package released fine for RHEL 8 previously, using qtbase5-dev and libqt5-widgets.

Why the entries are missing

#50896 built these keys by merging existing ones:

I used gemini to combine the following existing rosdep keys: (and then reviewed it manually)
qt6-base-dev, qtbase5-dev, libqt5-widgets, libqt6widgets6t64

Two of those sources — qtbase5-dev and libqt5-widgets — have a flat, unversioned rhel: entry, which covers every RHEL version including 8. Collapsing that into a version-keyed map produced {'*': qt6, '8': null, '9': qt5}, dropping RHEL 8. The stated scope was "Rolling (and in the future Lyrical) use Qt5 on RHEL 9 / Ubuntu Noble, and Qt6 everywhere else", where RHEL 8 does not apply, so nothing in review would have flagged it.

So the null is an artifact of that collapse, not an assertion that Qt is unavailable on RHEL 8.

Every value here is already in use on RHEL 8

Each package name below is provided by an existing key whose rhel: entry is flat, and therefore already resolves on RHEL 8:

key	RHEL 8 value added	already provided on RHEL 8 by
qt-base-dev	qt5-qtbase-devel	qtbase5-dev, qt5-qmake, libqt5-opengl-dev
libqtwidgets	qt5-qtbase	libqt5-widgets, libqt5-core, libqt5-concurrent
libqtcore	qt5-qtbase	libqt5-core
libqtopengl	qt5-qtbase	libqt5-opengl
libqtgui	qt5-qtbase-gui	libqt5-gui
libqtsvg	qt5-qtsvg	libqt5-svg
qt-svg-dev	qt5-qtsvg-devel	libqt5-svg-dev

In every case the new RHEL 8 value is identical to the existing RHEL 9 value, which is the expected outcome: RHEL 8 and 9 both ship Qt5, and only '*' (RHEL 10 and newer) has Qt6.

Scope

All seven members of the family, rather than only the two that blocked our release — the omission is uniform across them and fixing a subset would leave the same failure waiting for the next package. #52673 is the precedent: it filled the equivalent missing jammy entry in qt-base-dev so that packages "correctly pick up the Qt5 or Qt6 version of this package, depending on which distro they are running." This is the RHEL 8 half of that same gap.

The other keys in base.yaml with rhel: '8': null are Qt6-only (qt6-*, libqt6*, qml6-module-*) and are correctly null, since RHEL 8 has no Qt6. They are untouched.

test/rosdep_formatting_test.py and test/rosdep_duplicates_test.py pass.

Assisted-by: Claude Code:claude-opus-5

[github-actions]

For changes related to rosdep:

• ✅ Platforms for new rosdep rules are valid

For changes related to yamllint:

• ✅ All new lines of YAML pass linter checks

[github-actions]

For changes related to rosdep:

• ✅ Platforms for new rosdep rules are valid

For changes related to yamllint:

• ✅ All new lines of YAML pass linter checks

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