validate_solutions.py: os.getenv('GITHUB_TOKEN', '') (#10546)

* validate_solutions.py: os.getenv('GITHUB_TOKEN', '')

@tianyizheng02

* updating DIRECTORY.md

* f this

---------

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>

DIRECTORY.md

@@ -373,6 +373,7 @@
   * [Electric Conductivity](electronics/electric_conductivity.py)
   * [Electric Power](electronics/electric_power.py)
   * [Electrical Impedance](electronics/electrical_impedance.py)
+  * [Ic 555 Timer](electronics/ic_555_timer.py)
   * [Ind Reactance](electronics/ind_reactance.py)
   * [Ohms Law](electronics/ohms_law.py)
   * [Real And Reactive Power](electronics/real_and_reactive_power.py)
@@ -622,6 +623,7 @@
   * [Is Ip V4 Address Valid](maths/is_ip_v4_address_valid.py)
   * [Is Square Free](maths/is_square_free.py)
   * [Jaccard Similarity](maths/jaccard_similarity.py)
+  * [Joint Probability Distribution](maths/joint_probability_distribution.py)
   * [Juggler Sequence](maths/juggler_sequence.py)
   * [Karatsuba](maths/karatsuba.py)
   * [Krishnamurthy Number](maths/krishnamurthy_number.py)
@@ -675,8 +677,8 @@
   * [Radians](maths/radians.py)
   * [Radix2 Fft](maths/radix2_fft.py)
   * [Remove Digit](maths/remove_digit.py)
-  * [Rkf45](maths/rkf45.py)
   * [Runge Kutta](maths/runge_kutta.py)
+  * [Runge Kutta Fehlberg 45](maths/runge_kutta_fehlberg_45.py)
   * [Segmented Sieve](maths/segmented_sieve.py)
   * Series
     * [Arithmetic](maths/series/arithmetic.py)