Check in spec/dummy/config/database.yml so CI can boot the dummy app

The file existed locally but was caught by a global gitignore rule
(database.yml everywhere), so it was never committed. CI checked the
repo out without it and every matrix cell failed at dummy-app boot:

  RuntimeError:
    Could not load database configuration.
    No such file - ["config/database.yml"]

Add a negation in the repo .gitignore so the one database.yml the
dummy app needs is tracked, and commit the file itself (sqlite3
:memory: for test, local file for development).

Author: Fivell

.gitignore

@@ -16,3 +16,7 @@
 /spec/dummy/db/*.sqlite3
 /spec/dummy/db/*.sqlite3-journal
 /spec/dummy/storage/
+
+# The dummy app's database.yml is checked in — override a global
+# ignore rule that excludes "database.yml" everywhere by default.
+!/spec/dummy/config/database.yml

spec/dummy/config/database.yml

@@ -0,0 +1,11 @@
+test:
+  adapter: sqlite3
+  database: ":memory:"
+  pool: 5
+  timeout: 5000
+
+development:
+  adapter: sqlite3
+  database: db/development.sqlite3
+  pool: 5
+  timeout: 5000