Remove workflow YAML generation process

[victorlin]

Context

.github/workflows/pathogen-repo-ci.yaml is generated from .github/workflows/pathogen-repo-ci.yaml.in using devel/explode-yaml, and similarly for pathogen-repo-build.

.github/devel/explode-yaml

Lines 2 to 6 in 729df6d

	# Explode YAML with anchors & references to YAML without them, using yq¹, for
	# GitHub Action's sake².
	#
	# ¹ <https://github.com/mikefarah/yq>
	# ² <https://github.com/actions/runner/issues/1182>

This doesn't work well with dependabot, which only edits the generated files (see d4cfac5).

Motivation

GitHub now supports YAML anchors (docs, September 2025 blog post).

Proposal

Remove the workflow YAML generation process added in edd3290.

[victorlin]

After opening #157, I found that our use of merge keys isn't supported.

PR-triggered error:

Invalid workflow file: .github/workflows/ci.yaml#L53
error parsing called workflow
".github/workflows/ci.yaml"
-> "./.github/workflows/pathogen-repo-build.yaml"
: (Line: 23, Col: 18): Unrecognized named-value: 'github'. Located at position 1 within expression: github.repository, (Line: 408, Col: 5): Unexpected value '<<', (Line: 408, Col: 5): There's not enough info to determine what you meant. Add one of these properties: cancel-timeout-minutes, container, continue-on-error, defaults, env, environment, outputs, runs-on, secrets, services, snapshot, steps, timeout-minutes, uses, with, (Line: 414, Col: 5): Unexpected value '<<', (Line: 414, Col: 5): There's not enough info to determine what you meant. Add one of these properties: cancel-timeout-minutes, container, continue-on-error, defaults, env, environment, outputs, runs-on, secrets, services, snapshot, steps, timeout-minutes, uses, with, (Line: 420, Col: 5): Unexpected value '<<', (Line: 420, Col: 5): There's not enough info to determine what you meant. Add one of these properties: cancel-timeout-minutes, container, continue-on-error, defaults, env, environment, outputs, runs-on, secrets, services, snapshot, steps, timeout-minutes, uses, with

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