Bump minimal SQLAlchemy version to 1.3

[Nothing4You]

What do these changes do?

Bump minimal SQLAlchemy version to 1.3.
According to https://www.sqlalchemy.org/download.html all older versions are EOL, 1.3 is still in maintenance state.

Are there changes in behavior for the user?

aiomysql[sa] now requires SQLAlchemy version 1.3.

Checklist

• Documentation reflects the changes
• Add a new news fragment into CHANGES.txt

[codecov]

Codecov Report

Merging #815 (1b6ebb3) into master (57d5b8e) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #815   +/-   ##
=======================================
  Coverage   92.72%   92.72%           
=======================================
  Files          38       38           
  Lines        5569     5569           
  Branches      943      943           
=======================================
  Hits         5164     5164           
  Misses        317      317           
  Partials       88       88           

Flag	Coverage Δ
ubuntu-latest_3.10_mariadb-10.3	89.27% <ø> (ø)
ubuntu-latest_3.10_mariadb-10.4	89.27% <ø> (ø)
ubuntu-latest_3.10_mariadb-10.5	89.26% <ø> (ø)
ubuntu-latest_3.10_mariadb-10.6	89.26% <ø> (ø)
ubuntu-latest_3.10_mariadb-10.7	89.26% <ø> (ø)
ubuntu-latest_3.10_mariadb-10.8	89.26% <ø> (ø)
ubuntu-latest_3.10_mysql-5.7	89.96% <ø> (ø)
ubuntu-latest_3.10_mysql-8.0	91.34% <ø> (ø)
ubuntu-latest_3.11-dev_mariadb-10.3	89.24% <ø> (ø)
ubuntu-latest_3.11-dev_mariadb-10.4	89.24% <ø> (ø)
ubuntu-latest_3.11-dev_mariadb-10.5	89.22% <ø> (ø)
ubuntu-latest_3.11-dev_mariadb-10.6	89.22% <ø> (ø)
ubuntu-latest_3.11-dev_mariadb-10.7	89.22% <ø> (ø)
ubuntu-latest_3.11-dev_mariadb-10.8	89.22% <ø> (ø)
ubuntu-latest_3.11-dev_mysql-5.7	89.92% <ø> (ø)
ubuntu-latest_3.11-dev_mysql-8.0	91.30% <ø> (ø)
ubuntu-latest_3.7_mariadb-10.3	88.67% <ø> (ø)
ubuntu-latest_3.7_mariadb-10.4	88.67% <ø> (ø)
ubuntu-latest_3.7_mariadb-10.5	88.66% <ø> (ø)
ubuntu-latest_3.7_mariadb-10.6	88.66% <ø> (ø)
ubuntu-latest_3.7_mariadb-10.7	88.66% <ø> (ø)
ubuntu-latest_3.7_mariadb-10.8	88.66% <ø> (ø)
ubuntu-latest_3.7_mysql-5.7	89.40% <ø> (ø)
ubuntu-latest_3.7_mysql-8.0	90.87% <ø> (ø)
ubuntu-latest_3.8_mariadb-10.3	89.32% <ø> (ø)
ubuntu-latest_3.8_mariadb-10.4	89.32% <ø> (ø)
ubuntu-latest_3.8_mariadb-10.5	89.30% <ø> (ø)
ubuntu-latest_3.8_mariadb-10.6	89.30% <ø> (ø)
ubuntu-latest_3.8_mariadb-10.7	89.30% <ø> (ø)
ubuntu-latest_3.8_mariadb-10.8	89.30% <ø> (ø)
ubuntu-latest_3.8_mysql-5.7	90.00% <ø> (ø)
ubuntu-latest_3.8_mysql-8.0	91.37% <ø> (ø)
ubuntu-latest_3.9_mariadb-10.3	89.17% <ø> (ø)
ubuntu-latest_3.9_mariadb-10.4	89.17% <ø> (ø)
ubuntu-latest_3.9_mariadb-10.5	89.15% <ø> (ø)
ubuntu-latest_3.9_mariadb-10.6	89.15% <ø> (ø)
ubuntu-latest_3.9_mariadb-10.7	89.15% <ø> (ø)
ubuntu-latest_3.9_mariadb-10.8	89.15% <ø> (ø)
ubuntu-latest_3.9_mysql-5.7	89.85% <ø> (ø)
ubuntu-latest_3.9_mysql-8.0	91.22% <ø> (ø)

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